Cost-Effective Water Saving Devices & Practices

GG67GUIDE

COST-EFFECTIVE WATERSAVING DEVICES ANDPRACTICES

GOOD PRACTICE: Proven technology and techniques for profitable environmental improvement

© Crown copyright. First printed March 1997. This material may be freely reproduced except for sale or advertising purposes.

Printed on paper containing 75% post-consumer waste.

COST-EFFECTIVE WATERSAVING DEVICES ANDPRACTICES

This Good Practice Guide was produced by the

Environmental Technology Best Practice Programme

Prepared with assistance from:

Ashact Ltd

All industrial and commercial organisations use water. Most organisations take water for grantedand few know exactly how much water they are using. Many organisations are paying more inwater and effluent charges than they need to and can probably reduce their water consumptionsimply and inexpensively.

What company can afford to ignore the savings that could be achieved by following the advice givenin this Good Practice Guide? Other companies, including their competitors, may have alreadyimplemented water saving measures and could be paying less in water and effluent charges per unitof production or service.

This Guide describes a range of cost-effective water saving devices and practices - some withpaybacks of only a few days. It highlights the typical water savings that can be achieved forindustrial and commercial applications and explains how to identify the most appropriate devicesand practices for specific equipment, processes or sites.

Water saving devices and practices applicable to industrial and commercial sites are described in twoseparate Sections. However, operators of industrial sites are also advised to read the practical adviceon saving water at commercial sites. The suggested actions are summarised in a series ofcomprehensive tables, which include an indication of the potential costs and payback period.

The potential cost savings and other benefits of reducing water consumption are illustrated inexamples from industrial and commercial sites.

There is an Action Plan near the end of this Guide to help focus on the ideas that are most relevantto individual organisations.

The water saving devices and practices described in this Guide are intended to be implemented aspart of a systematic water saving campaign. Such a campaign is described in Good Practice Guide(GG26) Saving Money Through Waste Minimisation: Reducing Water Use, available free through theEnvironmental Helpline on 0800 585794.

S U M M A R Y

Water, water, everywhere and no one stops to think.

Section Page

1 Introduction 1

1.1 How can this Guide help? 1

1.2 Carrying out a water use survey 2

1.3 The tale of one cubic metre of water 3

2 Choosing water saving devices and practices 4

2.1 First considerations 4

2.2 Estimating potential savings 4

2.3 The impact of water savings on operating costs 8

2.4 Setting the project budget 8

2.5 Identifying appropriate water saving devices and practices 9

2.6 Identifying project costs 9

2.7 Worked example for a commercial site 10

3 Water saving devices and practices for industrial sites 12

3.1 General water use 12

3.2 Cleaning and washdown 16

3.3 Process plant 18

4 Water saving devices and practices for commercial sites 22

4.1 General water use 22

4.2 Toilets 22

4.3 Sinks 24

4.4 Showers 25

4.5 Gardening 25

4.6 Laboratories 26

4.7 Garages 26

5 Measuring water use and flow 27

6 Action plan 30

Appendices

Appendix 1 A typical water saving campaign 31

Appendix 2 Water and effluent charges 33

Appendix 3 Estimating pumping, energy and treatment costs 34

Appendix 4 Converting between systems of units 37

Appendix 5 Further reading 38

C O N T E N T S

1.1 HOW CAN THIS GUIDE HELP?

Water is used in many different ways by industry and commerce. Most organisations think theyknow where their water goes. But do they really know?

Companies need to ask themselves the following questions:

Are we using too much water?

Are we paying too much in effluent charges?

Have we tried saving water?

Could we save any more water?

Have our competitors implemented water saving measures?

This Good Practice Guide describes a variety of cost-effective water saving projects with paybacksfrom a few days to over one year. The Guide is intended to help identify the most appropriate watersaving devices and practices for specific equipment, processes or sites.

Sections 1 and 2 highlight the significant potential savings from different applications and explainhow to identify the best water saving options for individual organisations. Generic water uses andtypical applications are described in Section 3 (industry) and Section 4 (commerce); suitable controlequipment is suggested together with guidance on its application. Tables 7 - 9 (industrial sites) andTable 10 (commercial sites), which should be used in conjunction with Sections 3 and 4 respectively,summarise the guidance on water saving devices and practices.

Operators of industrial sites are advised to read the whole Guide, whereas those whose operationsare predominantly commercial, will find Section 4 most useful.

Inclusion of specific water saving devices and practices in this Guide is not a recommendation fortheir universal implementation. Cost-effective application is often site-specific. In particular, watersaving devices and practices proposed for industrial processes should be evaluated, prior toimplementation, by those with a working knowledge of the processes.

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On-line water and effluent monitoring at Walkers Snack Foods highlighted a process problemwhich was costing £720/day. It was fixed in three days. If Walkers had waited for the waterbill, the fault might have gone undetected for four months. By then, it would have cost theCompany over £80 000. If Walkers had not known how much water was normally used toproduce each bag of crisps, £250 000/year could have been lost without Walkers realising it.

Mainswater flow measurement, which included a connection into an existing on-linemonitoring system for process control, cost less than £2 000 to install.

Also, effluent billing used to be based on incoming metered water. Following a change tobilling on the basis of effluent flow measurement, which cost less than £3 000 to install,effluent billing has been reduced by £24 000/year.

Before adopting any water saving device or practice, companies should:

■ evaluate the technical issues;

■ carry out a COSHH* assessment;

■ consider the health and safety implications;

■ examine the financial considerations.

To help, this Guide highlights other benefits and possible disadvantages which should be taken intoaccount when selecting a water saving device.

The identification and evaluation of cost-effective water saving devices and practices should be partof a wider water saving campaign. The phases and steps involved in a typical water savingcampaign are indicated in Appendix 1, and further advice and information are available through theEnvironmental Helpline on 0800 585794.

1.2 CARRYING OUT A WATER USE SURVEY

Before beginning a water saving campaign, water and effluent costs should be looked at to makesure it is worth taking action.

Information about comparative water consumption in various sectors has been collated by manytrade associations. Relative water use is also discussed in some of the Environmental PerformanceGuides available through the Environmental Helpline and these will provide a useful benchmark.

As a rule-of-thumb, for sites that have not previously tried to save water, reductions of 20% in waterand effluent bills are usually achievable at little or no cost. As much as 40%, or more, might beachievable if projects with paybacks of up to two years are included.

Before being able to identify how and where water can be saved, an understanding is needed ofhow, where and why water is used on each particular site. These objectives can be achieved bycarrying out a water use survey and developing a water balance for a site.

First, the following questions should be asked:

How many projects, modifications and additions have been carried out since the lastwater survey at a site?

Who performed the last survey and how thorough was it?

Are the drawings up to date?

Good Practice Guide (GG26) Saving Money Through Waste Minimisation: Reducing Water Useoutlines a systematic approach to the development of a water balance and reducing the costsassociated with water use and wastewater disposal. This includes the drawing up of a water massbalance and allocating consumption. GG26 is one of a series of three complementary Good PracticeGuides on waste minimisation. The other two cover the use of raw materials (GG25) and teams andChampions (GG27). All these Guides are available free through the Environmental Helpline.

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Practical Tip

It will be extremely useful later if during the water use survey:

■ schematic diagrams of the water and effluent systems are produced;

■ pipework and valves are labelled.

* Control of Substances Hazardous to Health (COSHH) Regulations 1994

Regular surveys, eg annual, are essential to keep water and effluent systems in good order.

A survey of water distribution systems and points of use typically reveals:

■ unidentified connections;

■ cross connections;

■ broken valves;

■ incorrectly set valves;

■ leaks.

A survey of water use and patterns of use typically reveals:

■ excessive or unnecessary use;

■ unknown use;

■ unauthorised use.

A survey of effluent discharges and routes to sewer typically reveals:

■ clean water discharges direct to effluent;

■ unauthorised discharges to effluent;

■ unnecessary surface water discharges to effluent;

■ sources of potential failure of effluent discharge consents.

Details of how to measure water flow are given in Section 5.

1.3 THE TALE OF ONE CUBIC METRE OF WATER

For those without a technical background it is sometimes helpful to illustrate flow as detailed below,to give an indication of what water might be costing a company.

A flow rate of 1 m3/hour of water is approximately equivalent to:

■ the flow from a garden hose; or

■ filling a 9 litre (2 gallon) bucket in half a minute; or

■ half a pint/second.

The range of ‘water only’ and ‘water and effluent’ costs vary throughout the UK. The 1996 - 1997water and effluent charges levied in different areas of England, Scotland and Wales are given inAppendix 2. Prices are lower in Scotland, but the situation is changing. For current informationplease contact the local water authority.

Water companies charge by the cubic metre (m3). The lowest and highest charges in England andWales for water only in 1996 were 48 - 77 pence/m3 and for water and effluent 62 - 134 pence/m3.

So at 1996 prices, a flow rate of 1 m3/hour will cost between:

■ 48 pence and £1.34 every hour; or

■ £12 and £32 every day; or

■ £80 and £225 every week; or

■ £4 205 and £11 740 every year.

Remember, one cubic metre of water weighs one tonne and one litre of clean water weighs onekilogramme*.

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* The density of clean water is 1 g/ml or 1 000 kg/m3

2.1 FIRST CONSIDERATIONS

Before starting to identify and evaluate water saving devices and practices, the following need to beagreed:

■ a target for net savings based on preliminary water survey (Section 1.2);

■ payback periods for any water saving projects.

And the following should be considered:

How are savings in water use estimated?

What impact will water savings have on overall operating costs?

How much can be spent on water saving measures?

How can appropriate water saving devices and practices be identified?

How much will it cost?

Appendix 1 contains a flow chart showing the steps involved in a typical water saving project. Thiswill help implement a water reduction programme. In practice, the individual steps are simple.However, to produce the most cost-effective water saving system, each step must be carried out inorder.

2.2 ESTIMATING POTENTIAL SAVINGS

Once the water balance has been established and water use in each area of the site is understood,the water saving team can start to identify water saving opportunities. Advice on the selection andmanagement of waste minimisation teams is given in Good Practice Guide (GG27) Saving MoneyThrough Waste Minimisation: Teams and Champions, available free through the EnvironmentalHelpline on 0800 585794.

Table 1 shows the typical percentage reductions for commercial and industrial applications whichcan be assumed when estimating potential savings. Although these are typical realistic reductions,they will vary between applications and sites and should not be relied upon for design purposes.Table 1 will, however, help to rule out projects which are non-starters.

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C H O O S I N G W AT E R S AV I N GD E V I C E S A N D P R A C T I C E S

2

Water saving initiative Typical reduction

Per project Per site

Commercial applications

Toilets, men’s toilets, showers and taps 40% (combined)

Industrial applications

Closed loop recycle 90%

Closed loop recycle with treatment 60%

Automatic shut-off 15%

Countercurrent rinsing 40%

Spray/jet upgrades 20%

Re-use of wash water 50%

Scrapers 30%

Cleaning in Place (CIP) 60%

Pressure reduction See Fig 1

Cooling tower heat load reduction See Fig 2

Table 1 Typical achievable reduction in water use

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Fig 1 Effect of pressure reduction on water use at jets, nozzles and orifices

Fig 2 Effect of heat load reduction on make-up water requirement for a cooling tower

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5

4

3

2

1

0 2 4 6 8 10

Percentage reduction in water distribution pressure

Red

uct

ion

in w

ater

usa

ge

at

jets

, no

zzle

s an

d o

rifi

ces

(%)

20

15

10

5

0 5 10 15 20

Percentage reduction in heat load on cooling tower

Red

uct

ion

in m

ake-

up

w

ater

req

uir

emen

t (%

)

Figs 3 and 4 provide estimates, at 1996 prices, of the significant annual losses from taps, joints onpipes, seals in pumps, hoses and valves. Although the figures are taken from real water surveys,they are intended for guidance only. The leaks and other losses of individual organisations may bedifferent.

In Figs 3 and 4, ‘water only’ refers to water use either where the water does not enter the drains orat sites which have a fixed effluent charge. In Fig 3 the range of ‘water only’ and ‘water andeffluent’ costs are based on the lowest and highest charges in England and Wales in 1996, ie 48 - 77 pence/m3 and 62 - 134 pence/m3 respectively.

In Fig 4, ‘minimum annual water cost’ refers to the cost of water in areas with low water charges,while ‘maximum water and effluent cost’ represents the amount levied in areas with high water andeffluent charges. These annual costs are calculated on the basis of 48 pence/m3 for water only and134 pence/m3 for water and effluent (1996 prices).

1996 - 1997 water and effluent charges levied in different areas of England, Scotland and Wales aregiven in Appendix 2.

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2 Two drops/second

1 minute loss 18 ml

Annual loss 9.5 m3

Annual water only cost £5 - £7

Annual water and effluent cost £6 - £13

Drops breaking into a stream

1 minute loss 59 ml

Annual loss 31 m3



2 mm stream

1 minute loss 277 ml

Annual loss 146 m3



3 mm stream

1 minute loss 638 ml

Annual loss 336 m3



5 mm stream

1 minute loss 1 litre

Annual loss 528 m3



Fig 3 Water losses from an open tap

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Practical Tip

A training programme should increase employee awareness of:

■ the cost of filling sinks;

■ the cost of using hoses;

■ the cost of overfilling process tanks;

■ the importance of identifying, reporting and mending leaks.

One drop/second

Hourly loss 0.5 litres

Annual loss 4.7 m3

Minimum annual water only cost £2

Maximum annual water and effluent cost £6

0.1 litre/minute

Hourly loss 6 litres

Annual loss 53 m3

Minimum annual water only cost £25

Maximum annual water and effluent cost £71

0 - 4 litres/minute

Hourly loss 0 - 240 litres

Annual loss 0 - 2 100 m3

Minimum annual water only cost £1 010

Maximum annual water and effluent cost £2 810

7 - 14 litres/minute

Hourly loss 420 - 840 litres

Annual loss 3 680- 7 360 m3



30 - 66 litres/minute

Hourly loss 1 800 - 4 000 litres

Annual loss 15 770 - 34 690 m3



700 litres/minute

Hourly loss 4 200 litres

Annual loss 367 920 m3



Union

Flange

Pumpshaft seal

Valve

1/2" Ballvalve

2" Pipe

1" Hose

Fig 4 Typical water losses from leaking valves, joints, pipes, pump seals and hoses

2.3 THE IMPACT OF WATER SAVINGS ON OPERATING COSTS

Cost savings can arise from reductions in:

■ water use;

■ on-site water pumping and associated maintenance;

■ water treatment, eg lower chemical costs and filter backwash;

■ water heating or cooling requirements;

■ effluent pumping;

■ effluent treatment;

■ effluent cooling requirements;

■ effluent discharge.

Savings can also arise from:

■ a delayed requirement for additional capacity for water storage;

■ increased production without having to upgrade the water supply system;

■ less product discharged as effluent;

■ lower capital investment in future effluent treatment plant;

■ reduced corrosion and improved working conditions through the elimination of leaks.

2.4 SETTING THE PROJECT BUDGET

Once the potential impact of water savings on overall operating costs has been estimated, it is usefulto work out how much money could reasonably be spent on the project. This will eliminate obviousnon-starters. One simple way of doing this is to work out the ‘Maximum Project Budget’ (MPB).

Maximum Project Budget (£) = Calculated saving (£/year) x Required payback period (years)

The overall capital and operating costs of any water saving project must be less than the MPB inorder to achieve the required payback. Operating costs should also be low enough to remainattractive in the long-term.

An organisation may use other methods of financial appraisal to determine the viability of proposedprojects. If so, it may be wise to seek advice from the financial department.

2.4.1 Worked example

This fictitious example illustrates the ‘project budget first’ approach. For the initial evaluation, thefollowing assumptions are made:

■ implementing the water saving project would reduce water use on a particular item of plantby 50%;

■ this corresponds to a 16% reduction in water use for that area of the factory.

Table 2 shows the net cost of increased production with and without the water saving project. Using13 290 m3/year less water would reduce operating costs by £78 907 - £64 481 = £14 426. This isnot money saved, as the costs have not yet been taken into account. To achieve a one year payback,the MPB will be £14 426, ie, the combined capital and first year operating costs of the new watersaving devices and practices must be less than £14 426.

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Item Without water saving With water saving

Production (including planned increase) 1 444 500 units/year 1 444 500 units/year

Specific water use 0.0575 m3/unit 0.0483 m3/unit

Total annual use 83 060 m3 69 770 m3

Water and effluent charge 95 pence/m3 95 pence/m3

Water and effluent bill £78 907 £66 281

Other reductions in operating costs (chemicals, 0 (£1 800)

pumping) associated with lower water use

Net cost £78 907 £64 481

Table 2 Net costs of increased production with and without water saving in a fictitious company

2.5 IDENTIFYING APPROPRIATE WATER SAVING DEVICES ANDPRACTICES

Once the water saving team has identified potentially attractive opportunities for saving water, thenappropriate water saving devices and practices can be investigated.

Water saving devices and practices in industrial applications are considered in Section 3 andsummarised in Tables 7, 8 and 9.

Water saving devices and practices in commercial applications are considered in Section 4 andsummarised in Table 10.

To identify appropriate water saving devices and practices for evaluation at a site, start with thetables and then turn to the associated text for further explanation.

2.6 IDENTIFYING PROJECT COSTS

Given the Maximum Project Budget, the costs associated with the necessary equipment now needto be evaluated. In practice, this may be an on-going process as water savings and costs usuallydepend on the equipment selected.

For accurate evaluation, it is best to obtain quotations for the equipment costs and estimated watersavings from potential suppliers or installation contractors. Also, the costs of the initial water surveyand management time need to be allocated.

Project costs occur in two stages:

■ Implementation

- design and project management;

- equipment purchase;

- installation and commissioning of all equipment and instrumentation;

- disruption of work during installation and commissioning.

■ Operation

- employee training;

- utilities use and maintenance;

- disposal of wastes from any treatment processes;

- monitoring (including water quality);

- reporting.

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Appendix 3 gives some guidance on how to estimate:

■ the effect of reduced water use on pumping costs;

■ water heating and cooling costs;

■ on-site water treatment costs.

2.7 WORKED EXAMPLE FOR A COMMERCIAL SITE

This example from a fictitious small hotel highlights the importance of evaluating possible watersaving measures for their economic viability.

A 20 bedroom hotel with a restaurant and a bar (open to non-residents) has decided to investigateways of reducing its water and sewage bills. These are based on a charge of £1.34/m3 of waterused. The hotel has also decided to implement water saving projects for which the expectedpayback is less than two years.

Following a water use survey and brainstorming session to discuss ideas, the hotel has:

■ ruled out evaluation of dishwashers and other washing machines as these are new;

■ ruled out sinks which are used for food, glass and utensil washing as these require controlledflow;

■ ruled out baths and showers because these are relatively new;

■ discovered that bedroom washbasins are used much less frequently than others elsewhere inthe building;

■ realised that the flushing volume of the toilets with cisterns could be reduced from nine litresto about seven litres;

■ discovered that a pair of men’s toilets in the bar toilet share a cistern and could thus share aflush control unit.

Tables 3 and 4 summarise the survey findings.

Area of hotel Washbasins WC Men’s

Rooms Other toilets toilets

Bedrooms 20 - 20 0

Restaurant toilet - 3 3 1

Bar/reception and toilet - 5 5 2

Kitchen staff toilet - 2 2 0

Total 20 10 30 3

Table 3 Possible sources of water savings in the hotel

Current water use (litres/day) Washbasins WC Men’s Total

Rooms Other toilets toilets

Bedrooms (1.25 people/room) 680 - 900 - 1 580

Restaurant toilet - 512 346 864 1 722

Bar/reception and toilet - 1 344 864 1 134 3 342

Kitchen staff toilet - 410 144 - 554

Total water use (litres/day) 680 2 266 2 254 1 998 7198

Total water use (m3/day) 0.68 2.266 2.254 1.998 7.198

Annual cost (for 360 days) £328 £1 093 £1 087 £964 £3 472

Table 4 Current water use at the hotel

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Possible water saving devices (see Section 4) included:

■ fitting percussion (push) taps on all washbasins (50% reduction);

■ installing cistern volume adjusters in the WC toilets (16% reduction);

■ installing passive infrared flush controls in the men’s toilet areas (70% reduction).

Table 5 shows the potential savings from these measures.

Future water use (litres/day) Washbasins WC Men’s Total

after water saving measures Rooms Other toilets toilets

Bedrooms (1.25 people/room) 340 - 756 - 1 096

Restaurant toilet - 256 291 261 808

Bar/reception and toilet - 672 726 340 1 738

Kitchen staff toilet - 205 121 - 326

Total water use (litres/day) 340 1 133 1 894 601 3 968

Total water use (m3/day) 0.34 1.133 1.894 0.601 3.968

Present annual cost (for 360 days) £328 £1 093 £1 087 £964 £3 472

Annual predicted cost (for 360 days) £164 £547 £914 £290 £1 915

Annual reduction in water £164 £546 £173 £674 £1 557

and sewerage bill

Table 5 Predicted savings from three water saving measures

When the project costs were compared with the expected savings, the conclusions were:

■ conversion to percussion taps on washbasins in frequent use is cost-effective;

■ conversion to percussion taps on bedroom washbasins is not cost-effective in this case;

■ fitting cistern bags to WC toilets is cost-effective;

■ fitting passive infrared control systems in urinal areas is cost-effective.

The estimated project economics are summarised in Table 6.

Washbasins WC Men’s Total of

Rooms Other toilets toilets cost-effective

projects

Total number of devices required 40 20 30 2 52

Cost of each device £30 £30 £4 £120 £154

Total cost (including installation) £1 800 £840 £150 £350 £1 340

Expected saving £164 £546 £173 £674 £1 393

Payback (years) 11 1.5 0.9 0.5 about 1

Table 6 Economic analysis of possible water saving measures at the hotel

The total cost of the three water saving measures identified as cost-effective is £1 340. Savings of£1 393 are predicted, giving an overall payback of about one year.

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This Section suggests cost-effective devices and practices to reduce water consumption at industrialsites. The advice is summarised in Tables 7 - 9. Case Studies are used to illustrate the savings thatcan be achieved.

Water saving devices and practices proposed for an industrial process should be evaluated,on a case-by-case basis, by someone with a working knowledge of the process.

3.1 GENERAL WATER USE

The following Section should be read in conjunction with Table 7. Look for the sub-headings in thecolumn labelled ‘Method’.

3.1.1 Monitoring

Although water flow rates can be displayed on meters fitted to pipelines, these are often out ofsight. Transmitting a flow signal to the process operator can allow more effective use of theinformation. Some existing turbine type flowmeters - with simple dial displays - can be uprated in situ to provide a pulsed flow signal. This signal can either be transmitted to the site control systemor, with suitable cables and an interface board, be logged in and displayed on a standard officecomputer.

A company’s water use could be nearly zero during ‘silent’ hours. Does this apply to your company?

3.1.2 Leakage identification and elimination

Leaks can arise from:

■ damaged pipeline connections, flanges and fittings;

■ worn valves;

■ flooded floats (balls) on water tank or cistern valves;

■ corroded pipework and tanks.

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W AT E R S AV I N G D E V I C E S A N DP R A C T I C E S F O R I N D U S T R I A L S I T E S

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J W Lees and Company achieved savings of over £32 500/year by monitoring water flowsthrough the brewery and ensuring actual consumption was as close as possible to theoreticalconsumption. Payback was effectively instantaneous. For full details, see Good Practice CaseStudy (GC41), available free through the Environmental Helpline.

The electroplating company, N T Frost, reduced its water consumption by nearly 60 000m3/year, saving almost £45 000/year. Good housekeeping, use of flow monitors and someflow restrictors significantly reduced water use without any major modifications. The paybackperiod was six months. For details, see Good Practice Case Study (GC22), available freethrough the Environmental Helpline.

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Item/application Aim Method Description/ Equipment/ Applicability Other benefits Other factors Potential Potentialpurpose technique cost payback

Training for water Water saving Awareness by Make people Training All areas of use Med Medsaving awareness training conscious of the

cost of water use

Water saving Water saving Communication Comparison of use Discussion All areas of use Shared experience Med Medculture between users between similar users

Water use survey Water saving Identify and Site-wide survey Site records and All areas of use Med Shortmeasure flow measurements

General water use Minimisation Monitoring On-line water Flow meters/ Processes using Med Short(Section 3.1) use display transmitters water

Leakage identification Inspection and repair Regular inspection Pipes/tanks/glands/ Reduced Med Medand elimination of equipment gaskets/flanges maintenance

Overflow Avoiding overflows Level controllers Tanks Reduced risk Med Medidentification and of floodingelimination

Use of block valves Using block valves Block valves Plant with preset Consistent Low Shortinstead of preset instead of control or adjustable flow process efficiency control valves for valves avoids need to of water isolation change preset positions

Flood prevention Automatic shut-off Rupture valves Pressurised systems Site protection Low-med Risk Assesmentof excess flow required

Tamper prevention Preventing Straps/chains/locks Widespread Consistent Low Medunauthorised process efficiencyadjustment

Plan temporary Avoiding waste during Examination of Pre-construction, Low Shortsupplies abnormal activities temporary water during process

supplies modification, etc

Reduce undesirable Maintaining water at Insulation Long distribution Reduced Med Medheat loss or gain required temp. systems energy costs

Trace heating High temp. Med Med

Heating/cooling Acute water temp. Equipment costs Med-high Med-longat point of use sensitivity

Table 7 Cost-effective water saving devices and practices for industrial sites: general water use

Potential costs and paybacks are for guidance only. Actual costs and paybacks will vary due to project-specific details.Potential cost: Low = Minor alterations to existing plant (£0 - a few £100s); Med = Some alterations to existing plant (a few £100s - a few £1 000s); High = Extensive alterations or new plant (many £1 000s).Potential payback: Short = Months; Med = Less than a year; Long = Over a year.

This Table should be read in conjunction with Section 3.1.

3.1.3 Overflow identification and elimination

Most overflows run to drain without being measured. However, the flow rate during overflow canbe as high as the delivery pumping flow rate.

Overflows are usually due to poor control. The following devices are usually adequate to avoidoverflows:

■ simple level sensors and on/off control systems for pumps;

■ shut-off valves.

3.1.4 Use of block valves instead of preset control valves for isolation

Many systems, eg liquid ring vacuum pumps, require preset water flow rates. The flow rate in suchsystems is usually adjusted by careful setting of a control valve. However, the same valve is oftenused to isolate the water supply and is not reset to the same position when flow resumes.

A simple and cheap solution is to:

■ fit a quarter turn isolation valve, eg ball valve;

■ preset the existing flow control valve to the optimum flow rate;

■ remove the handwheel from the flow control valve;

■ use the quarter turn valve for isolation as required.

3.1.5 Flood prevention

If the pipework fails and floods the site, you will probably be charged for the water you wasted. Youwill also suffer the inconvenience and damage caused by the flood. Blow-out preventers, which arenot expensive, could save most of the costs of a flood.

3.1.6 Tamper prevention

Fitting straps, chains or padlocks should eliminate unauthorised valve operation. Leather or clothstraps which can be cut easily are preferable where emergency use of the water supply is required.The removal of handwheels from isolation valves tempts operators to use spanners. This is badpractice as the valves frequently become inoperable due to spindle damage.

3.1.7 Plan temporary supplies

Temporary water supplies are often necessary during process modifications and may be required formany months. Such supplies are often taken from the nearest available water system, which maybe at a higher pressure than the normal supply. Using water at a higher pressure leads to equipmentsuch as sprays and jets using higher than normal quantities of water.

Pressure reduction valves may be required for temporary water supplies.

3.1.8 Reduce undesirable heat loss or gain

In situations where the temperature of the water is crucial to its suitability for use and water is usedintermittently, long pipework can be lagged and/or trace heated to reduce heat losses or heat gain.This avoids the practice of water being run to drain until it achieves the correct temperature.

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At one site, the need to route the drinking water supply through hot areas made the waterunpleasant to drink. The solution was to install a chiller at the point of use rather than runningwater to drain continuously. The cost of £400 was paid back in less than two months. Analternative could be to provide bottled water in a refridgerator.

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Item/application Aim Method Description/ Equipment/purpose technique

Cleaning and Minimisation Flow restriction/ Reducing Valves, orifices, washdown pressure control instantaneous flow pressure reducing

at point of use valves

Countercurrent Re-use of rinse water Tanks/pumpsrinsing

Sprays/jets Appropriate application Nozzlesof water

Spray nozzles

High pressure spray packages

Automatic Use of water only Solenoid valves in supply shut-off when needed pipelines

Actuated valves in pipelines

Jets/spray guns on hoses

Re-use of wash Re-use of wash water Tanks/pumpswater in other areas

Substitution Scrapers/ Sweeping up Dry cleaning squeegees/ brushes of slurries methods

Short term Cleaning in Place (CIP) Countercurrent re-use Proprietary plantre-use technology of rinse water with

multiple re-use ofchemical cleaners

Long term Recycle after Treatment of Filtration/re-use treatment wastewater to an sedimentation

acceptable standardfor re-use

Centrifugation/flotation

Biological treatment

Ion exchange

Distillation/stripping

Absorption/adsorption

Table 8 Cost-effective water saving devices and pra

Potential costs and paybacks are for guidance only. Actual costs and paybacks will vary due to project-specific details.Potential cost: Low = Minor alterations to existing plant (£0 - a few £100s); Med = Some alterations to existing plant (a few £100s - a few £1 000s); HigPotential payback: Short = Months; Med = Less than a year; Long = Over a year.


Applicability Other benefits Other factors Potential Potentialcost payback

Variable or Low Shortintermittent supply pressure or demand

Multi-stage unit Water quality High Longprocesses

Widespread Improved cleaning Low-med Short-med

Widespread Improved cleaning Spray/mist drift Low-med Short-med

Washing processes Improved cleaning Power Med-high Short-medconsumption

Small bore pipes Essential water Low-med Medrequirement Solenoid power supply

Large bore pipes Essential water Med Medrequirement

Widespread More efficient Theft of spray guns Low V. shortapplication

Widespread Cross contamination/ Med Short-medwater quality control

Large areas Possible re-use Dry collection system Low Shortof materials

Processes with Hygienic plant/ Water quality High Short-medfrequent cleaning minimal downtime

for cleaning

Coarse solids Waste disposal Med Med-longremoval/phase Water qualityseparation

High quality solids Waste disposal High Med-longremoval/phase Water qualityseparation

Removal of dissolved Waste disposal High Med-longbiodegradable solids Water quality

Removal of dissolved Waste disposal High Med-longcontaminants Water quality

Solvent recovery By-product Waste disposal High Med-longWater quality

High quality Disposal of High Med-longtreatment, solvent spent absorbentrecovery, removal of toxic substances, colour, etc

actices for industrial sites: cleaning and washdown

gh = Extensive alterations or new plant (many £1 000s).


Variable or Low Shortintermittent supply pressure or demand

Multi-stage unit Water quality High Longprocesses

Widespread Improved cleaning Low-med Short-med

Widespread Improved cleaning Spray/mist drift Low-med Short-med

Washing processes Improved cleaning Power Med-high Short-medconsumption

Small bore pipes Essential water Low-med Medrequirement Solenoid power supply

Large bore pipes Essential water Med Medrequirement

Widespread More efficient Theft of spray guns Low V. shortapplication

Widespread Cross contamination/ Med Short-medwater quality control

Large areas Possible re-use Dry collection system Low Shortof materials

Processes with Hygienic plant/ Water quality High Short-medfrequent cleaning minimal downtime

for cleaning

Coarse solids Waste disposal Med Med-longremoval/phase Water qualityseparation

High quality solids Waste disposal High Med-longremoval/phase Water qualityseparation

Removal of dissolved Waste disposal High Med-longbiodegradable solids Water quality

Removal of dissolved Waste disposal High Med-longcontaminants Water quality

Solvent recovery By-product Waste disposal High Med-longWater quality

High quality Disposal of High Med-longtreatment, solvent spent absorbentrecovery, removal of toxic substances, colour, etc

actices for industrial sites: cleaning and washdown


Successful switching methods include:

■ limit switches;

■ signals from existing process controls;

■ signals from existing interlocks.

However, the water isolation system must ‘fail safe’ where supplies are essential, eg for largegearbox cooling.

Trigger-operated spray guns on hoses can achieve significant reductions in water use because theflow stops when the hose is put down.

3.2.5 Re-use of wash water

Used wash water is often flushed down the drain on the basis that it has been ‘used’. Carefulexamination of the quality and availability of wash water, together with an understanding of waterrequirements elsewhere on-site, may reveal opportunities for re-use.

Typical final uses of wash water include:

■ first washdown/rinse of floors and containers (inside or outside);

■ making up raw material slurries (not applicable to the food or drink industries).

3.2.6 Scrapers/squeegees/brushes

During cleaning, large quantities of water from hoses are frequently used to wash slurries fromfloors and walls down the drain. Hand-held scrapers will move most of the slurry across the floorefficiently.

The combined use of scrapers, brushes and hoses can reduce the time taken to clean an area.Removing slurries from surfaces before they start to dry or pre-wetting dry areas can reduce:

■ the volume of water needed for washdown;

■ the time taken.

Pipelines can often be cleaned effectively using ‘pigging’ systems. A pig is typically an engineeredplug or ball which fits inside the pipe and is pushed through mechanically or hydraulically to clearmaterial ahead of the pig.

3.2.7 Cleaning in Place (CIP) technology

CIP systems are used to clean process plant in situ. They typically re-use final rinse water for firstrinses and re-use concentrated cleaning chemicals many times for intermediate washing cycles.

3.2.8 Recycle after treatment

Re-use of used water is often feasible following suitable treatment to remove unacceptableimpurities. Possible treatment technologies include:

■ filtration;

■ clarification/sedimentation;

■ centrifugation;

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A small washdown hose can use 1 m3 of water every hour. If this is hidden under a piece ofequipment and forgotten for a week (it does happen), then at a combined water and effluentcost of 80 pence/m3 this will cost £19.20/day or £134.40/week. A trigger-operated spray guncosts about £70; the payback period - allowing £35 for fitting - could be as low as 51/2 days.

■ flotation;

■ ion exchange;

■ distillation/stripping;

■ absorption/adsorption.

However, it should be remembered that:

■ a small flow to drain may be required to control impurities which are not removed by thetreatment process(es);

■ treatment processes give rise to sludges, dirty filters, etc which will require controlled disposal;

■ closed-loop flows may increase in temperature and thus require cooling.

The costs associated with on-site water treatment are outlined in Appendix 3.

3.3 PROCESS PLANT

The following Section should be read in conjunction with Table 9. Look for the sub-headings in thecolumns labelled ‘Item/application’ and ‘Method’.

3.3.1 Liquid ring vacuum pumps

This type of pump uses a continuous supply of water to provide the seal. There may also be arequirement for some water to cool bearings or lubricate the shaft seal. Such pumps, which needa continuous supply of seal water during operation, consume large volumes of water.

The seal water is typically heated by 15°C in the pump and, in some cases, is discharged directly todrain. This water can often be recovered for re-use. However, direct recirculation as sealing wateris limited by its temperature; the higher the water temperature, the lower the efficiency of thevacuum pump especially when drawing air saturated with water vapour. Seal water may requirecooling and other treatment before re-use. Installing cyclone pre-separators on the vacuum side ofthe pump can help to minimise contamination of the seal water.

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3

Water minimisation measures are saving Chloride Motive Power Batteries Ltd £110 000/year(payback period of 1 - 2 years).

■ Replacement of a wet filtration system with a membrane filter saved £12 000/year.

■ Use of a crossflow filtration system allowed water recycling, saving £9 000/year.

■ Re-use of treated effluent at various stages of the process saved £50 000/year.

For details see Industry Example 2 from Good Practice Guide (GG26), available free through theEnvironmental Helpline.

The use of ion exchange technology to treat effluent from an electroplating shop at AmphenolLtd allowed the water to be re-used in a closed-loop system. The Company saved £108 000in the first year alone. The reduction in water consumption was 89%, with a payback of lessthan 16 months. For details see Good Practice Case Study (GC24), available free through theEnvironmental Helpline.

19

Item/application Aim Method Description/ Equipment/ Applicability Other benefits Other factors Potential Potentialpurpose technique cost payback

Liquid ring Recycle Recycle sealing Re-use of sealing Tanks/pumps/ Widespread Energy savings Seal water High Medvacuum pumps water water after treatment separators/cooling from cooling quality control

seal water Seal water temperature

Substitution Change to Avoid use of water Mechanical Widespread Liquid trap High Medmechanical system vacuum pumps

Cooling towers Minimisation Automatic Operation at Conductivity-based Widespread Reduced Med Shortblowdown control maximum acceptable control chemicals use

TDS* concentration

Cooling load Minimise evaporation Process Widespread Reduced Med Medreduction and blowdown optimisation chemicals use

Heat recoveryelsewhere

Substitution Use of alternative Avoid evaporation Air blast High cooled water Monitoring High Med-longcooling processes of water temp. requirements

(temp above 40°C)

Heat exchangers Widespread Waste heat High Medcould be used elsewhere

Heat exchangers Long-term Closed-loop Re-use Tanks/pumps/ Widespread Heat sink/ High Med-longre-use water cycle heating source/ cooling tower/

cooling source water quality

Hydraulic Minimisation Cooling water Optimise water use by Bulb-and-capillary Widespread Essential cooling Low-med Shortpower packs flow control from varying water flow operated flow requirement

oil temp. depending on oil control valves temp.

Long-term Closed-loop Re-use after cooling Tanks/pumps/ Large installations Cooling tower/ High Longre-use cooling water cycle cooling source water quality

Table 9 Cost-effective water saving devices and practices for industrial sites: process plant

Potential costs and paybacks are for guidance only. Actual costs and paybacks will vary due to project-specific details.Potential cost: Low = Minor alterations to existing plant (£0 - a few £100s); Med = Some alterations to existing plant (a few £100s - a few £1 000s); High = Extensive alterations or new plant (many £1 000s).Potential payback: Short = Months; Med = Less than a year; Long = Over a year. *TDS = total dissolved solids


section

3

Options for controlling the temperature of the seal water include:

■ simple systems which bleed off warm water and top up with fresh cold water;

■ cooling towers;

■ integrated heat recovery systems.

Significant energy savings may be achieved by cooling seal water as this could enable the vacuumpump to be run at lower speeds.

For detailed information on the optimum use of water in liquid ring vacuum pumps and the re-useof seal water, see Good Practice Guide 83, Energy Efficient Liquid Ring Vacuum Pump Installationsin the Paper Industry. This Guide is available free from the Energy Efficiency Enquiries Bureau at ETSUon 01235 436747.

For some duties, the liquid ring vacuum pump could be replaced with a purely mechanical vacuumpump. This may have the added attraction of energy savings.

3.3.2 Cooling towers

Automatic blowdown control

Cooling towers operate with a small flow of water moving from the cold well to drain (blowdown).This is intended to keep the level of dissolved solids to a minimum. Build-up of solid deposits in thetower packing or plant cooling system can reduce cooling efficiency.

Cooling towers are often operated with a constant blowdown flow. This flow can be minimised byusing automatic control systems which measure the total dissolved solids content of the coolingwater.

Cooling load reduction

Cooling towers require fresh make-up water to replace evaporative losses and blowdown. Theamount of make-up water depends directly on the cooling load. Minimising the cooling load byusing the waste heat elsewhere in the factory will reduce the use of fresh water as make-up water.

For a 1 000 kW cooling duty, a typical cooling tower uses 2 m3/hour of fresh water and produces0.75 m3/hour of blowdown to drain. These amounts will depend on the air temperature and relativehumidity.

Spray/mist recovery

Cooling towers also lose water as spray/mist. This water loss depends on the effectiveness, or eventhe existence, of a mist eliminator.

In a cooling tower operating with optimised automatic blowdown control, losses of usable water aresmall as the spray loss is effectively blowdown. However, in a cooling tower operated with a fixedblowdown, spray loss represents a loss of usable water. It is likely to be more cost-effective to installautomatic blowdown control than to upgrade the spray/mist eliminator.

Use of alternative cooling processes

Conventional cooling towers can be replaced by air blast coolers in situations where ‘cooled’ watertemperatures of up to 40°C can be tolerated during the summer months.

20

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3C Davidson and Sons saved £65 000/year by cooling and re-using water from the site’s liquidring vacuum pumps. The payback period was 14 weeks. In addition, electricity costs fell by£173 000/year. For details see Good Practice Case Study 127, available free from the EnergyEfficiency Enquiries Bureau at ETSU on 01235 436747.

In some cases, cooling systems can be integrated with other systems to cool one stream and heatanother. Heat exchange with incoming cold water can often achieve lower temperatures thancooling towers.

3.3.3 Heat exchangers

Closed-loop water cycle

Heat exchanger cooling water does not always have to be discharged direct to drain. After cooling,the water may be re-usable. A small flow to drain, or a filter, may be required to control the build-up of contaminants. Most sites already make use of the energy content of the hot water streamfrom heat exchangers.

3.3.4 Hydraulic power packs

Cooling water flow control from oil temperature

Large hydraulic power packs typically require a supply of cold water to cool the hydraulic oil. Often,the flow of cooling water is uncontrolled.

The cooling water flow can be controlled by a control valve linked to a thermostat in the oil. Simple,adjustable bulb-and-capillary operated flow control valves are available which do not requireelectrical supplies. If cooling is essential to avoid damage to equipment, the valve should be set tofail open rather than closed.

Closed-loop cooling water cycle

Hydraulic-power-pack oil coolers are often plumbed into the nearest water supply and dischargedto drain. Cooling water for the oil could be obtained from, and returned to, alternative sources, egsite process cooling water systems. The heat load is relatively small when compared with processcooling duties.

21

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Installation of cooling water recycle loops for reciprocating air compressors at Stoves plcreduced water consumption by 30%. The water saving was worth about £35 000/year andthe payback period was around three months. For details see Industry Example 5 from GoodPractice Guide (GG26), available free through the Environmental Helpline.

Wallcoverings manufacturer, Borden Decorative Products Ltd, has reduced water consumption atits Lancashire site by nearly 40%. Most of the reduction was due to good practice and theinstallation of a cooling loop recycle in place of an existing open loop system. The payback periodon the installation was seven months. For details see Industry Example 6, also from Good PracticeGuide (GG26).

This Section suggests cost-effective devices and practices to reduce water consumption atcommercial sites. The advice is summarised in Table 10. A Case Study from a wholesale fooddistributor is used to illustrate the savings that can be achieved.

The following Sections should be read in conjunction with Table 10. Look for the sub-headings inthe column labelled ‘Method’.

Contact a plumber or building maintenance service for information about how to obtain the watersaving devices mentioned.

4.1 GENERAL WATER USE

4.1.1 Automatic/manual isolation of water supply

Passive infrared (PIR) sensors can be used to detect activity in areas and thus control water suppliesto suit the activity. These sensors typically use long-life batteries, lasting 3 - 4 years. Replacementbatteries should be obtained from the original supplier.

PIR systems are particularly appropriate for washrooms and toilets and can be extended to controllighting and fans as well as water supplies.

Control of water supplies using a timer is suitable when work hours can be predicted. A cheapalternative is to use a single valve for area isolation which is closed manually by the ‘last person out’.

4.2 TOILETS

4.2.1 Flush control

The rate at which men’s toilet cisterns fill andempty is often controlled by a needle valve.Water consumption can be significantly improvedby PIR controlled devices.

However, the toilets must be flushed at theminimum frequency necessary to remain hygienic.When retrofitting flush controls in existing toilets,readers are advised to consult their supplier aboutthe minimum flushing frequency desirable fortheir site’s specific circumstances. Control offlushes is required under current water by-laws.Flush controls are now fitted as standard on men’stoilets in new commercial buildings.

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WAT E R S AV I N G D E V I C E S A N DP R A C T I C E S F O R C O M M E R C I A L S I T E S

4

Fig 5 Flush control using passive infrared sensor

Installation of infrared flush controldevices in 2 000 buildings reduced a largetelecommunications company’s waterconsumption by over one million m3/year.

23

Item/application Aim Method Description/ Equipment/purpose technique

Training for water Water saving Awareness Make people conscious Trainingsaving awareness by training of the cost of water use

Water saving culture Water saving Communication Comparison of use Clubsbetween users between similar users

Water use survey Water saving Identify and measure Site-wide survey Site records, flow measureme

General water use Minimisation Automatic/manual Shut off water when PIR sensor and solenoid(Section 4.1) isolation of water supply not required

Seven day timer

Manual valve last person out

Toilets (Section 4.2) Minimisation Men’s toilet Optimised flushing PIR sensor and solenoidflush control frequency

Optimised flushing rate Flow limiting valves/orifices

Reduced cistern Reduced water Smaller cisternsvolume volume per flush

Cistern volume adjuster (CVA

Substitution Chemical Chemical treatment Waterless men’streatment of toilet effluent toilet

Sinks (Section 4.3) Minimisation Reduced bowl filling Use of a smaller Small sinkworking volume

Automatic supply Use of water only Self-closing tapsshut-off when required

Showers (Section 4.4) Minimisation Flow restriction Reduced flow shower Low flow shower

Gardening (Section 4.5) Minimisation Sprays/jets Appropriate Spray nozzlesapplication of water

Automatic Use water only Solenoid valvessupply shut-off when required

Spray guns

Abandon grass Do not water grass. Nothingwatering Leave it to recover

during autumn

Minimise Reduce evaporation Nothingevaporation by watering during the

coolest part of the day

Water released in required Permeable pipearea by underground permeable pipe

Rainwater collection Collection of rainwater Pipes/containersfrom guttering

Laboratories (Section 4.6) Minimisation Condensers Using minimum flow Nothing

Substitution Mechanical Alternative provision Mechanicalvacuum pumps of vacuum vacuum pumps

Garages (Section 4.7) Minimisation Sprays/jets Appropriate Spray nozzlesapplication of water

High pressure spray packagesLong term Recycle through Treatment of wash Proprietary plantre-use treatment water to an acceptable

standard for re-use

Table 10 Cost-effective water saving de

Potential costs and paybacks are for guidance only. Actual costs and paybacks will vary due to project-specific details.Potential cost: Low = Minor alterations to existing plant (£0 - a few £100s); Med = Some alterations to existing plant (a few £100s - a few £1 000s); HigPotential payback: Short = Months; Med = Less than a year; Long = Over a year.

This Table should be read in conjunction with Section 4


All areas of use Med Med

All areas of use Shared experience Med Med

ent All areas of use Med Short

Wash rooms Reduced flood risk Med Med

Fixed work hours Med Short-med

Distribution systems Med Short-med

Men’s toilets Med Short-med

Out-of-date Hygiene requirements Med Short-med

New installations Med Med

A) Old toilets Hygiene requirements Low Short

Remote areas Solid waste High Meddisposal/hygiene

New installations Washing requirements Med Med

Widespread Reduced flood risk Med Med

Widespread Energy savings Med Med

Widespread Low Med

Widespread Low Med

Widespread Low Short

Widespread Some areas may suffer Zero Instant

Widespread Overtime Zero Instant

Widespread Med Med

Widespread Med Med

Widespread Condenser efficiency Zero Instant

Widespread Liquid trapping High Long

Improved cleaning Low Short-med

s Improved cleaning High Short-medVehicle Waste disposal High Med-long

evices and practices for commercial sites



All areas of use Med Med

All areas of use Shared experience Med Med

ent All areas of use Med Short

Wash rooms Reduced flood risk Med Med

Fixed work hours Med Short-med

Distribution systems Med Short-med

Men’s toilets Med Short-med

Out-of-date Hygiene requirements Med Short-med

New installations Med Med

A) Old toilets Hygiene requirements Low Short

Remote areas Solid waste High Meddisposal/hygiene

New installations Washing requirements Med Med

Widespread Reduced flood risk Med Med

Widespread Energy savings Med Med

Widespread Low Med

Widespread Low Med

Widespread Low Short

Widespread Some areas may suffer Zero Instant

Widespread Overtime Zero Instant

Widespread Med Med

Widespread Med Med

Widespread Condenser efficiency Zero Instant

Widespread Liquid trapping High Long

Improved cleaning Low Short-med

s Improved cleaning High Short-medVehicle Waste disposal High Med-long

evices and practices for commercial sites


4.4 SHOWERS

4.4.1 Flow restriction

Low flow, high velocity showers use water efficiently. Typical, conventional shower use is 35 litres.Power showers use substantially more water.

4.5 GARDENING

4.5.1 Sprays/jets

When watering plants and gardens, water can be misused by spraying over too wide or too narrowan area. Sprays and jets allow water to be evenly distributed where it is actually needed.

4.5.2 Automatic supply shut-off

A garden hose can use 1 m3 of water every hour. If the hose is hidden under a bush and forgotten,then at a water cost of 55 pence/m3, this will cost £13.20/day. A lightweight, trigger-operated spraygun costs about £25 (1996 prices). The payback in this case - allowing £15 for fitting - would beabout three days.

4.5.3 Abandon grass watering

Unless green lawns are essential, grass does not need to be watered regularly. Most areas of grassin the UK will recover to a respectable green colour during the autumn without any artificialwatering during the summer. Only well-drained or shallow areas may suffer.

Sprinkler users can expect to either pay an additional fee or have their water supply metered.

25

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4

Booker Belmont Wholesale Ltd manages utility use at the 160 Booker Cash & Carry wholesaleoutlets in the UK. Water costs represented less than 5% of utility costs and were originallygiven a low priority. However, closer examination revealed that significant savings could beachieved quickly at many depots by installing simple, low-cost devices.

Booker installed the following water saving devices at 109 selected branches across the UK:

■ 975 percussion taps which closed after one to 30 seconds;

■ 235 cistern volume adjusters;

■ 115 flush controls.

The benefits of this water saving project, which cost around £74 000 to implement, include:

■ average reduction in water use and wastewater generation of over 65%;

■ total cost savings of £106 700/year for the 109 depots;

■ average reduction in annual water and effluent charges of over £970/depot;

■ payback period of under nine months.

Full details of this successful water saving project are given in Good Practice Case Study (GC61),Low-cost Measures Save Water at a Multi-site Company, and is available free through theEnvironmental Helpline on 0800 585794.

4.5.4 Minimise evaporation

Evaporation from soil and plants can be minimised by:

■ watering in the cool of the evening;

■ subsurface watering with permeable pipes;

■ using mulches.

4.5.5 Rainwater collection

Rainwater from guttering is usually adequate for use on gardens and may also be suitable inuntreated form for other low-grade uses. Drums or tanks can be used to collect the rainwater withminor modifications to downpipes. Attention should be given to diverting any overflow back to therainwater drain.

Untreated rainwater should not be used for drinking.

4.6 LABORATORIES

4.6.1 Condensers

Condensers are usually connected to a tap and set to operate at full flow.

4.6.2 Vacuum pumps

Many small vacuum pumps used in laboratories are driven by mains water and require a continuoussupply of water to operate. Such pumps can usually be replaced with mechanical vacuum pumps,but with attention to liquid trapping to protect the pump.

4.7 GARAGES

Spray systems can improve water use in vehicle washing. High pressure jetting systems can beefficient, but require careful use.

Washing water can be recycled following treatment in proprietary equipment.

26

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4

Water flow can be measured either in pipelines or in channels. The numerous options for flowmeasurement each have their own advantages and disadvantages.

The following questions should be considered before selecting a flow measurement system orcontacting a supplier of flow measurement equipment:

■ What accuracy is required?

■ Will the flow rate obtained by ‘bucket and stopwatch’ methods be sufficiently accurate?

■ How big are the pipes and can they be opened to insert an invasive flow measurementsystem?

■ What is the temperature, pressure and range of speed of the water?

■ Is the water clean or dirty? If dirty, what is the nature of the contamination?

■ Is the pipework old and corroded? Corrosion can cause problems for strap-on systems.

■ Is the pipework insulated or trace heated?

■ Will a pressure drop across an invasive metering element be acceptable?

■ Is a signal for output to on-line monitoring or recording systems required?

Where flows are accessible, measuring the time taken to fill a bucket or other container is usuallyan extremely effective, cheap and simple method of measuring flows. Bucket and stopwatchmeasurements of clean water flows can be speeded up using a spring balance, as one litre of cleanwater weighs one kg. Don’t forget the weight of the bucket.

Water use in toilets can be estimated from the frequency of use and cistern volume. WC cisternvolumes can be calculated from measurements obtained by tying up the ballcock gently, flushingand filling the cistern from a graduated bucket.

Use in washbasins can be estimated by temporarily disconnecting the ‘U’ bend and then runningthe waste into a large, graduated plastic bucket while using clean water to simulate normal use, egwashing hands.

Details of other commonly used flow measurement techniques are summarised in Table 11.Electrical signals produced by flow measurement systems can be collected in data loggers for trendanalysis.

27

M E A S U R I N G W AT E R U S E A N D F L O W

5

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5

Sensor element Type Principle Applicability Common problems

Turbine Invasive Rotation of turbine Clean water Solids or solventsblades by flow Pipes

Rotameter Invasive Variable area Clean water Must be verticalPipes

Orifice Invasive Pressure differential Clean water Solids may block pressurePipes tappings

Magnetic Invasive Distortion of Clean or dirty water Must remain full*magnetic field Pipes

Thermal dilution Invasive Rate of cooling Clean or dirty waterPipes or channels

Ultrasonic - Invasive/ Vector addition Clean or slightly Might not work in dirty time-of-flight Non-invasive of velocities dirty water water

Pipes

Ultrasonic - Invasive/ Reflections from Dirty water Will not work in Doppler Non-invasive particles in water Pipes clean water

Ultrasonic + Invasive Doppler for flow Dirty water Small weir may be requiredpressure Pressure for depth Pipes or channels

or sewers

Weir Invasive Level upstream Clean or dirty water Settling solids will of weir Channels require removal

Flume Invasive Level upstream Clean or dirty water Settling solids will of flume Channels require removal

Bucket and - Time taken to Clean or dirty water ‘Spot’ flow measurementstopwatch collect a known

volume

Drop tank test - Rate of change of ‘Spot’ flow measurementdepth in tank

* Some new systems will measure flow in part-full pipes

Table 11 Commonly used flow measurement techniques

Other specialised systems include oval rotors, venturi tubes, Pitot tubes, averaging Pitot tubes andvortex shedders.

Turbine meters usually provide a direct visual display of cumulative flow. Instantaneous flow signalscan usually be acquired from optional sensors which bolt onto the turbine casing and provide pulsedelectrical outputs.

Installing a few inexpensive turbine-type water meters at key points in the water distribution systemcan enhance the results obtained from a water use survey. At 1996 prices, a flowmeter for a 0.5 inch (1.25 cm) pipe costs about £60 and for a 2 inch (5 cm) pipe the cost is about £260.

Numerous versions of inexpensive orifice meters which give direct readings of instantaneous floware available.

Strap-on ultrasonic flowmeters can give good results, but older pipework may cause problems.

Levels at weirs or flumes, and hence the flow, can be measured non-invasively by ultrasonic distancemeasuring systems or invasively by pressure gauges. Foam on the surface can cause problems withultrasonic systems. Large diameter diaphragm-based pressure systems are available for use in caseswhere solids could block standard pressure transmitters. Such systems are also available withhygienic fittings.

Drop tank tests can be used to calibrate flow measurement systems.

28

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5

Another method of measuring the water level - a variant of the pressure technique - uses a smalldip tube to gently blow air bubbles in the water from below the surface. The amount of excess airpressure required to expel air is related to the depth of water above the end of the dip tube; thedeeper the water, the higher the pressure required to expel air.

The accuracy of flow measurement equipment is affected by the proximity of:

■ valves;

■ bends;

■ other items which affect the flow.

The selection and application of flow measurement systems are described in An Introductory Guideto Flow Measurement by R C Baker and published by Mechanical Engineering Publications Ltd in1989 (ISBN 0-85298-670-X).

Flow which falls from the end of horizontal pipes or channels can be estimated by critical depthmeasurements. The tables, equations and other guidance needed to calculate flow from anestimate of critical depth are given in A Handbook of Hydraulics by Brater, King and Lindell, 7th edition, McGraw Hill (ISBN 0-07007-247-7).

29

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Identification and implementation of cost-effective water saving devices and practices should becarried out as part of a campaign to minimise water use and wastewater generation at your site. Asystematic approach to waste minimisation is described in Good Practice Guide (GG26) SavingMoney through Waste Minimisation: Reducing Water Use, available free through the EnvironmentalHelpline on 0800 585794.

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A C T I O N P L A N6

Find out how much your organisation is paying in water and effluent charges.

Carry out a water use survey for your site.

Develop a water balance for your site.

Agree a target for water saving.

Estimate potential savings from reducing water use and effluent generation.

Identify other benefits from saving water.

Decide how much it is worth spending on water saving projects.

Identify and evaluate appropriate water saving devices and practices.

Identify project costs.

Consider the impact of the water saving measures on your particular industrialprocess.

Implement cost-effective water saving devices and practices.

If necessary, obtain help. The Environmental Helpline (0800 585794) can:

send you copies of relevant Environmental Technology Best Practice Programmepublications;

suggest other sources of information;

provide free up-to-date information on a wide range of environmental issues,legislation and technology;

arrange for a specialist to visit your company if you employ fewer than 250 people.

A typical water saving campaign involves the four phases summarised in Fig A1.

Fig A1 The four phases of a typical water saving campaign

The main steps involved in a typical water saving campaign are shown in Fig A2. These steps arebroadly similar for both industrial and commercial sites.

31

A T Y P I C A L W AT E R S AV I N GC A M PA I G N

Appendix 1

appx

A1

PHASE 1 - Initiation

■ Involve staff and appoint the leader (‘Champion’) of the water saving team.

■ Find out about water saving devices and their application, eg read this Good PracticeGuide, contact the Environmental Helpline on 0800 585794 for advice.

■ Talk to other interested people in the organisation.

■ Develop a simple programme.

■ Allocate sufficient resources.

PHASE 2 - Water use survey and development of the water balance

■ Identify where, how and why water is used.

■ Identify the water quality requirement at each point of use.

■ Determine the water quality and availability at each point of discharge.

PHASE 3 - Evaluation of water saving options

■ Evaluate current and future water costs by area or item of equipment.

■ Identify and evaluate cost-effective water saving devices and practices.

■ Carry out trials of likely options.

PHASE 4 - Implementation

■ Train staff (if necessary).

■ Implement cost-effective water saving devices and practices.

■ Monitor the implemented devices and practices.

■ Communicate successes and savings to employees.

■ Obtain feedback from employees.

Fig A2 Water saving campaign flow chart

32

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A1

Start

Staff

Team and resources

Water usage survey

Brainstorming

Do it

Measure it

Report it

Continue

Outline a potential project

Estimate potential costreductions

Maximum Project Budget

Detailed design

Obtain accurate equipmentcosts and associated cost

reductions

Elimination by ruleof thumb methods.Is this an attractive

project?

Calculate real costs andcost reductions

Is this stillattractive?

IdeasGood Practice Guide

Manufacturer's informationSimilar units elsewhere

Other sources

Water and effluent costsProduction figures

Water saving potential

Target savingTarget payback

Manufacturers

Associated cost reductions

No

No

Yes

Yes

Table A1 shows charges typical of those levied by water companies and authorities in England,Scotland and Wales in 1996 - 1997. The figures are only indicative and should not be used fordetailed evaluation of a water savings project. Readers are advised to contact their local watercompany (water authority in Scotland) for information relevant to their site.

The charges shown in Table A1 include only the flow-related elements of the effluent charges(reception and volume) since the water saving methods outlined in this Guide are aimed at volumereduction. The total effluent charges levied by individual water companies and authorities includean element for pollutant concentration.

Water company/ Water supply Effluent charges Total chargesauthority (pence/m3) (reception and volume only) (pence/m3)

(pence/m3)

Anglian 58 24 82

Northumbrian 53 27 80

North West 60 18 78

Severn Trent 63 25 88

Southern 55 34 89

South West 75 59 134

Thames 48 14 62

Wessex 68 21 89

Yorkshire 64 29 93

Welsh 77 19 96

West of Scotland Water Authority 44 13 57

(WOSWA)

East of Scotland Water Authority 30 N/A* 30

(EOSWA)

North of Scotland Water Authority** ~61 ~15 ~76

(NOSWA)

* Standing charge (changes in volume have no effect on effluent bill)** Approximate quantities

Table A1 Typical water and effluent charges levied in 1996 - 1997

NB The standing or fixed charge element of a water bill depends on meter size. For example, ifan office block has a 100 mm meter where an 80 mm meter would suffice, annual chargesmay be over £1 000 more than necessary.

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A2

W AT E R A N D E F F L U E N TC H A R G E S

Appendix 2

ESTIMATING THE EFFECT OF REDUCED WATER USE ON PUMPINGCOSTS

Pumping costs depend mainly on:

■ the mode of operation of the pumping system;

■ the flow being pumped;

■ the pressure at which it is being pumped.

Fixed speed pumps

Pumping costs for a pumping station with fixed speed pumps which start and stop to meet demandcan be estimated pro rata from the total flow and pump power consumption.

Variable speed pumps

Systems which use variable speed pumps to maintain either a constant liquid level (eg drainagesumps) or constant pressure (eg ring mains) require more thought.

Estimating the power consumption for variable speed systems is more complicated. For example,pumping at half the flow rate reduces the instantaneous power requirement to overcome the statichead (pressure or gravity) to half but reduces the instantaneous power requirement to overcome thedynamic head (friction) to approximately one eighth. The process also takes twice as long.

Potential reductions in pumping costs for variable speed pumping systems are best estimated - if thedata are available - from hours-run meters, measured power consumption and total flow.

Pump maintenance costs can be estimated pro rata from the hours run.

ESTIMATING WATER HEATING AND COOLING COSTS

The power required to heat or cool water is much easier to estimate. You need to know:

■ the required temperature difference (°C);

■ the flow rate (litres/second);

■ the density (kg/m3);

■ the heat capacity of the water (the heat capacity of clean water = 4.18 kJ/kg°C);

■ the cost of a kWh of heating or cooling.

As the density of clean water is 1 000 kg/m3, a flow rate of 1 litre/sec of clean water is equivalentto 1 kg/second.

∴ Power requirement (kW*)

= Flow rate (kg/second) x temperature difference (°C) x heat capacity (kJ/kg°C)

NB Dirty water may have a different density and heat capacity compared with clean water. Ifnecessary, this should be taken into account.

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A3

E S T I M AT I N G P U M P I N G , E N E R G YA N D T R E AT M E N T C O S T S

Appendix 3

* 1kW = 1 kJ/second

Heating costs can then be calculated from the utility unit cost.

The cost of cooling in a cooling tower can be estimated from the cost of the make-up andblowdown to drain. For every 1 000 kW, this amounts to approximately 2 m3/hour make-up waterand approximately 0.75 m3/hour of blowdown to effluent.

In most cases, the cooling tower fan power consumption can be ignored. This should remainconstant unless controlled by the water temperature.

The cost of cooling by refrigeration can be calculated directly from the refrigeration plant costs.

Calculation example for a cooling tower:

A study in a fictitious factory has identified a process modification which would result in a reductionof 100 kW in cooling load on an evaporative cooling tower. What is the estimated reduction inwater and effluent costs if the cooling tower operates for 330 days/year, the water charges are 55 pence/m3 and the effluent charges are 34 pence/m3?

Calculate the reduction in water usage for evaporation and blowdown pro rata:

Estimated reduction in water and effluent charges = £1 199/year + £202/year = £1 401/year

There will be small additional cost savings of a few pounds for water treatment chemicals.

The estimated cost reduction can be used in the calculation of the Maximum Project Budget.

35

appx

A3

Reduction in evaporation = 2 m3/hour x 100 kW/1 000 kW = 0.2 m3/hour

Reduction in blowdown = 0.75 m3/hour x 100 kW/1 000 kW = 0.075 m3/hour

Reduction in effluent generation = reduction in blowdown only = 0.075 m3/hour

Annual reduction in effluent generation = 0.075 m3/hour x 24 hours/day x 330 days/year = 594 m3/year

Annual reduction in effluent charges = 594 m3/year x £0.34/m3 = £202/year

Reduction in water usage = reduction evaporation + reduction in blowdown = 0.2 m3/hour + 0.075 m3/hour = 0.275 m3/hour

Annual reduction in water usage = 0.275 m3/hour x 24 hours/day x 330 days/year = 2 180 m3/year

Annual reduction in water charges = 2 180 m3/year x £0.55/m3 = £1 199/year

ESTIMATING ON-SITE WATER TREATMENT COSTS

The costs associated with water treatment prior to use or re-use include:

■ consumables;

■ effluent and solid waste disposal;

■ energy.

A typical ion exchange system, eg base exchange with salt solution regeneration, used to reduce thetotal hardness of mains water from 375 mg/litre (as calcium carbonate) to less than 10 mg/litre (ascalcium carbonate) uses the following resources to produce 1 m3 of usable treated water:

■ 1.05 m3 mains water;

■ 0.5 kg salt (typically £130/tonne at 1996 prices).

Treatment generates, for every 1 m3 of usable water, 0.05 m3 regeneration solution and rinse water,ie the process achieves a 95% yield of treated water, with 5% waste as effluent to drain. The latterwill incur effluent charges.

Actual regeneration solution consumption depends on the quality of the mains water.

Reverse osmosis and membrane water treatment systems typically generate 0.25 m3 of effluent/m3

usable treated water.

Where mains water is treated, the effluent usually affects only the volume elements of effluentcharges.

Other water treatment systems, such as neutralisation, require more detailed examination.

If you need help on how to calculate the costs associated with water treatment, seek advice orcontact the Environmental Helpline on 0800 585794.

36

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A3

To Convert From: To: Multiply By:

US gallons UK gallons 0.8327

UK gallons Cubic metres 0.0045

UK gallons/hour Cubic metres/hour 0.0045

UK gallons/minute Cubic metres/hour 0.2728

UK gallons/second Cubic metres/hour 16.36

Cubic metres/hour Litres/second 0.278

Litres/second Cubic metres/hour 3.6

Cubic metres Litres 1 000

Cubic metres of clean water Kilogrammes 1 000

Litres of clean water Kilogrammes 1

37

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A4

C O N V E R T I N G B E T W E E NS Y S T E M S O F U N I T S

Appendix 4

Further information about water saving devices and practices can be obtained from the followingpublications. This is not an exhaustive list.

The Water Friendly Garden, The Royal Horticultural SocietyCharles Baker Publishing Ltd.

Water Wise, Environment Agency (Jun 1996)Available on request from the Environment Agency’s Water Demand Management CentreHelpdesk on 01903 832073.

Cutting Water and Effluent Costs, John S Hills, Institution of Chemical Engineers, 1995(ISBN 0-85295-361-5)

Water Conservation - Government Action, Water Supply and Regulation Division,Department of the Environment (Aug 1995)

Available from the Water Supply and Regulation Division, Department of the Environmenton 0171 276 8120.

Green Office Manual, Earthscan/Kogan Page. Tel: 0171 278 0433.

The Green Office Guide, Macmillan Press, 1997.

Water and process industry trade journals may also give useful ideas and information aboutequipment for water saving projects. Ask your trade association to recommend appropriatejournals.

USEFUL PUBLICATIONS FROM THE ENVIRONMENTALTECHNOLOGY BEST PRACTICE PROGRAMME

Relevant publications available free through the Environmental Helpline on 0800 585794 include:

■ Good Practice Guide (GG25) Saving Money Through Waste Minimisation: Raw MaterialUse;

■ Good Practice Guide (GG26) Saving Money Through Waste Minimisation: Reducing WaterUse;

■ Good Practice Guide (GG27) Saving Money Through Waste Minimisation: Teams andChampions.

The development and benefits of a waste minimisation culture which include water minimisation aredescribed in Good Practice Case Study (GC19), Waste Minimisation Pays Major Dividends.

38

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A5

F U R T H E R R E A D I N GAppendix 5

Further information about water saving devices and practices can be obtained from the followingpublications. This is not an exhaustive list.

The Water Friendly Garden, The Royal Horticultural SocietyCharles Baker Publishing Ltd.

Water Wise, Environment Agency (Jun 1996)Available on request from the Environment Agency’s Water Demand Management CentreHelpdesk on 01903 832073.

Cutting Water and Effluent Costs, John S Hills, Institution of Chemical Engineers, 1995(ISBN 0-85295-361-5)

Water Conservation - Government Action, Water Supply and Regulation Division,Department of the Environment (Aug 1995)

Available from the Water Supply and Regulation Division, Department of the Environmenton 0171 276 8120.

Green Office Manual, Earthscan/Kogan Page. Tel: 0171 278 0433.

The Green Office Guide, Macmillan Press, 1997.

Water and process industry trade journals may also give useful ideas and information aboutequipment for water saving projects. Ask your trade association to recommend appropriatejournals.

USEFUL PUBLICATIONS FROM THE ENVIRONMENTALTECHNOLOGY BEST PRACTICE PROGRAMME

Relevant publications available free through the Environmental Helpline on 0800 585794 include:

■ Good Practice Guide (GG25) Saving Money Through Waste Minimisation: Raw MaterialUse;

■ Good Practice Guide (GG26) Saving Money Through Waste Minimisation: Reducing WaterUse;

■ Good Practice Guide (GG27) Saving Money Through Waste Minimisation: Teams andChampions.

The development and benefits of a waste minimisation culture which include water minimisation aredescribed in Good Practice Case Study (GC19), Waste Minimisation Pays Major Dividends.

38

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A5

F U R T H E R R E A D I N GAppendix 5

The Environmental Technology Best Practice Programme is a joint Department of Trade and

Industry and Department of the Environment initiative. It is managed by AEA Technology plc

through ETSU and the National Environmental Technology Centre.

The Programme offers free advice and information for UK businesses and promotes

environmental practices that:

■ increase profits for UK industry and commerce;

■ reduce waste and pollution at source.

To find out more about the Programme please call the Environmental Helpline on freephone

0800 585794. As well as giving information about the Programme, the Helpline has access to

a wide range of environmental information. It offers free advice to UK businesses on technical

matters, environmental legislation, conferences and promotional seminars. For smaller

companies, a free counselling service may be offered at the discretion of the Helpline Manager.

FOR FURTHER INFORMATION, PLEASE CONTACT THE ENVIRONMENTAL HELPLINE

0800 585794e-mail address: [email protected]

World wide web: http://www.etsu.com/ETBPP/

Documents

Cost-Effective Water Saving Devices & Practices