Liz Stokle

Senior Health Protection Nurse

North East Health Protection Unit

Guidance for Responding to Drinking Water Quality Failures in theNorth East of England, March 2012

Responsibilities of Health Protection Unit

Health Protection Agency Act 2004 HPA has a duty to protect the public from threats …infectious diseases and environmental hazards. 

Following Notification the HPU with the local authority is to provide public health advice to the water company …pertinent to the local community affected.

Significant threat to public health, the HPU has a duty to inform the appropriate Director of Public Health for the (PCT) responsible for the health of the population affected and then to work on mitigation.

Challenges for risk assessment

Raw water abstraction

Treated water

Nature of problem failure –

problems at WTW; burst main; discoloured water; loss of supply; failure of standard at any point in process

Challenges for risk assessment

Raw water abstraction

Treated water

Nature of problem/failure

Chemical and microbiological parameters

Microbiological parameters

Indicator Organisms

Coliforms

Faecal indicators:

E.Coli

Enterococci

C.Perfringens

Multiple variables

Coliforms

Alone or in conjunction with other organisms such as E.coli

Small numbers or high numbers

Other biological & chemical parameters

Cryptosporidium

Lead

Fluoride

Chlorine or lack of

Drinking water safety

“The significance of individual test results for each microbiological parameter at each location varies and a single positive result does not necessarily mean that water is unsafe [or safe] to drink.

Other information is required to assess water safety.”

Drinking Water Safety -Guidance to health and water

Professionals (DWI/HPA December 2009)

Risk Assessment

Severity of consequences of the hazard:

• Effect on human health not just

• Meeting health based standards and indicator parameter values

The risk associated with the hazard needs to be considered in the context of the particular situation/circumstances

Contextual issues

Point of failure

Nature of failure

Size of population affected

Nature of population affected

Current awareness of GI illness

Challenges for protecting health of population

Interpreting the information/evidence

Risk assessment appropriate to context

Implementing proportionate response

Launch of document

Failure of Prescribed Concentration or Value (PCV)

LA first response (response should be initiated at presumptive stage within 1 working day of receipt of event notification)

HPA first response (response should be initiated at presumptive stage within 1 working day of receipt of event notification)

Standard response(within 1 month)

1. Coliforms 1-50 per 100ml in the ABSENCE of E. coli (otherwise action as for E.coli)

Discuss circumstances and context of failure with NWL/HW e.g. burst main, contamination at service reservoir: Assess: chlorine levels, cause of failure, population at risk & any

currently known increase in gastrointestinal illness Consider whether site visit to implicated location is necessary (may

involve liaison with other LAs & water company for access if wide distribution area affected)

Agree NWL/HW actions

Discuss circumstances and context of failure with NWL/HW e.g. burst main, contamination at service reservoir: Assess: chlorine levels, cause of failure, population at risk & any

currently known increase in gastrointestinal illness via current HPU surveillance systems

Agree NWL/HW actions

NWL/HW to report outcome of any follow-up samples as soon as available

1a. Coliforms >50 per 100ml in the ABSENCE of E. coli (otherwise action as for E.coli)

Value >50 coliforms with or without E.coli is an indication of poor quality drinking waterAs above PLUS Any abnormal changes in colony counts Agree measures to investigate ‘integrity of the system’ Agree with Water supplier further investigations for faecal

contamination

Value >50 coliforms with or without E.coli is an indication of poor quality drinking waterAs above PLUS Any abnormal changes in colony counts Agree measures to investigate ‘integrity of the system’ Agree with Water supplier further investigations for faecal

contamination

NWL/HW to report outcome of any follow-up samples as soon as available

2. E.coli 1–10 per 100ml (without coliforms or with coliforms up to a level of 50)

As above PLUS consider if ‘boil water’ advice should be issued If ‘boil water’ advice agreed, also agree conditions required to remove

the boil water notice

As above PLUS consider if ‘boil water’ advice should be issued and document rationale If ‘boil water’ advice agreed, also agree conditions required to remove

the boil water advice

As above PLUS NWL/HW remove ‘boil

water’ advice when agreed conditions achieved

3. E. coli >10 per 100ml (especially where coliforms >50)

As above PLUS consider immediate check sampling from consumers taps in affected area to verify NWL/HW bacterial sample results

As above PLUS discuss context & boil water advice

4. Cryptosporidium oocysts (any number) and/or report of turbidity >1 NTU at water treatment works or >4 NTUs at customer tap(Continued over)

Discuss context of failure in relation to extra evidence of risk i.e. aware of: Cluster/increase in cases in affected area Ingress at treatment works or in distribution network Treatment failure or turbidity failure in treated waterWhere no extra evidence of risk (as described above) and failure level low i.e. <1 oocyst/10 litres Agree action for resampling and investigation of causeWhere extra evidence of risk exists (as described above) and/or failure significant numbers i.e. >1 oocyst/10 litres in treated water Consider boil water advice with NWL/HW Agree conditions required to remove the boil water notice Alert EHO colleagues to be vigilant for cases

Discuss context of failure in relation to extra evidence i.e. aware of: Cluster/increase in cases in affected area Ingress at treatment works or in distribution network Treatment failure or turbidity failure in treated waterWhere no extra evidence of risk (as described above) and failure level low i.e. <1 oocyst/10 litres Agree action for resampling and investigation of causeWhere extra evidence of risk exists (as described above) and/or failure significant numbers i.e. >1 oocyst/10 litres in treated water. Discuss with senior to: Consider boil water advice with NWL/HW Agree conditions required to remove the boil water advice Alert HPU staff to enhanced surveillance for cases

As above PLUS NWL/HW Remove

‘boil water’ advice when agreed conditions achieved

HPU enhanced surveillance for increase in community cases

NWL/HW to report outcome of investigation

Table 1: Response to notification from Northumbrian Water Limited or Hartlepool Water relating to failures of mains water samples or of events posing a threat to supply

[

Reported failure – Mains Water

Domestic property – programmed sample result:

42 presumptive coliforms

0 E.coli

Free chlorine 0.16 mg/l

Total Chlorine 0.25 mg/l

Failure of Prescribed Concentration or Value (PCV)

LA first response (response should be initiated at presumptive stage within 1 working day of receipt of event notification)

HPA first response (response should be initiated at presumptive stage within 1 working day of receipt of event notification)

Standard response(within 1 month)

1. Coliforms 1-50 per 100ml in the ABSENCE of E. coli (otherwise action as for E.coli)

Discuss circumstances and context of failure with NWL/HW e.g. burst main, contamination at service reservoir: Assess: chlorine levels, cause

of failure, population at risk & any currently known increase in gastrointestinal illness

Consider whether site visit to implicated location is necessary (may involve liaison with other LAs & water company for access if wide distribution area affected)

Agree NWL/HW actions

Discuss circumstances and context of failure with NWL/HW e.g. burst main, contamination at service reservoir: Assess: chlorine levels, cause

of failure, population at risk & any currently known increase in gastrointestinal illness via current HPU surveillance systems

Agree NWL/HW actions

NWL/HW to report outcome of any follow-up samples as soon as available

Table 2 : Response to failures of private water samples

Type of Failure- of Prescribed Concentration or Value (PCV)

Local Authority HPA first response(on receipt of notification from LA unless otherwise stated)

Long term response LA and/or HPU as indicated(> 1 month and up to the 5 year review of the

supply risk assessment)First response(within 3 working days of receipt of result unless otherwise stated)

Standard response (within 1 month of last result) Consider serving notice under regulation 18

1. Coliforms 1-5 per100ml in the ASBSENCE ofE. coli (if E. coli present action as for E. coli below)

Inform owner/person responsible for supply & advise on improvements & checks to system

Undertake an investigation and/or risk assessment

Provide further advice on any improvements required based on risk assessment

HPU not informed LA revise supply risk assessment

2. Coliforms -any number >5 per 100ml in the ASBSENCE ofE. coli (if E. coli present action as for E.coli below)

Inform owner/person responsible for supply & advise on improvements & checks to system

Undertake an investigation and/or risk assessment

Provide further advice on any improvements required based on risk assessment

Where number of coliforms >50/100ml persists after re-sampling inform HPU

Consider Boil Water Notice*

Where number of coliforms >50/100ml persists in resamples after improvements have been made, clarify with LA: Number of properties on supply Whether a ‘high risk’ supply e.g.

includes commercial food or public premises

Whether a private distribution system

Consider Boil Water Notice*

LA and HPU agree remedial action and follow-up

If Boil Water Notice in place agree criteria for lifting notice

HPU consider/continue enhanced surveillance for GI illness using routine surveillance or contacting local GPs according to size of failure

If re-samples passLA revise supply risk assessment as appropriate

3. E. coli 1-5 per 100ml Inform owner/person responsible for supply & advise on improvements & checks to system

Issue a Boil Water Notice Issue health advice to all

consumers

Undertake RA/investigation including sampling

Where E.coli persists in samples after improvements have been made:Discuss with HPU

Inform owner/person responsible for supply & advise on improvements & checks to system

Agree supply improvement actions with owner/person responsible for the supply

Where E.coli persists in samples after improvements have been made, as actions in 2 above PLUS Discuss cause of failure

Size and nature of population at risk

Any currently known increase in GI illness

Agree remedial action with LADiscuss boil water advice with LA and agree criteria for lifting the advice based on results & evidence that risks identified in risk assessment have been controlled

as 2 above PLUS HPU consider/continue enhanced

surveillance for GI illnessIf re-samples pass as 2 above PLUS LA revise supply risk assessment on

completion of any improvement works

Reported failure – Private Water

Domestic property – programmed sample result:

42 presumptive coliforms

0 E.coli

Free chlorine ?

Total Chlorine ?

Private Water Supply

2. Coliforms -any number >5 per 100ml in the ABSENCE ofE. coli (if E. coli present action as for E.coli below)

Inform owner/person responsible for supply & advise on improvements & checks to system

Undertake an investigation and/or risk assessment

Provide further advice on any improvements required based on risk assessment

Where number of coliforms >50/100ml persists after re-sampling inform HPU

Consider Boil Water Notice*

Where number of coliforms >50/100ml persists in resamples after improvements have been made, clarify with LA: Number of

properties on supply

Whether a ‘high risk’ supply e.g. includes commercial food or public premises

Whether a private distribution system

Consider Boil Water Notice*

LA and HPU agree remedial action and follow-up

If Boil Water Notice in place agree criteria for lifting notice

HPU consider/continue enhanced surveillance for GI illness using routine surveillance or contacting local GPs according to size of failure

If re-samples passLA revise supply risk assessment as appropriate

Coliforms in PWS

*Where failure relates to coliforms without evidence of E.coli consider history of supply (where available) in relation to evidence that this result may suggest potential danger to human health e.g. management of supply not effective – in such cases a boil water notice may be warranted

Private Water Supplies

3. E. coli 1-5 per 100ml

Inform owner/person responsible for supply & advise on improvements & checks to system

Issue a Boil Water Notice

Issue health advice to all consumers

Undertake RA/investigation including sampling

Where E.coli persists in samples after improvements have been made:Discuss with HPU

Inform owner/person responsible for supply & advise on improvements & checks to system

Agree supply improvement actions with owner/person responsible for the supply

Where E.coli persists in samples after improvements have been made, as actions in 2 above PLUS Discuss cause of failure

Size and nature of population at risk

Any currently known increase in GI illness

Agree remedial action with LADiscuss boil water advice with LA and agree criteria for lifting the advice based on results & evidence that risks identified in risk assessment have been controlled

as 2 above PLUS HPU consider/continue

enhanced surveillance for GI illness

If re-samples pass as 2 above PLUS LA revise supply risk

assessment on completion of any improvement works

Shared guidance in NE