Rainwater Harvesting in Oatley

Jim Vickery

Oatley Flora and Fauna SocietyMonday 27th October 2014

Introduction

Rainwater harvesting questions:• How much water will I need each day?•Where can the rainwater tank be installed

to maximise the area of the roof used to collect rainwater?• How much rain is going to fall onto the

roof?•Will the rain come in showers or storms?• Best size for the rainwater storage tank?

Typical domestic water usage: L/dayNo. of people 2 4 6

Economical toilet 36 72 108

Economical toilet & economical clothes washing machine

236 422 558

PLUS – water for the garden

Oatley NSW rainfall characteristics:• Drier than many Sydney suburbs• Misses out on the coastal rainfall that

only comes as far as King Georges Rd. • Rain from the west tends to go to the

north and to the south!

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100

120

IDEALDRYBIG EVENT

DAYS

TANK CONTENTS

%

Tank storage perform-ance

A reliable supply

QuarterAverage(1993 to

2013)1996 2004

Q1 280 mm

Q2 265 mm

Q3 184 mm

Q4 200 mm

Annual 929 mm

Estimate of the reliable draw based on:• 1996 – an average year for rainfall • 2004 – a very dry winter

QuarterAverage(1993 to

2013)1996 2004

Q1 280 mm 277 222

Q2 265 mm 295 76

Q3 184 mm 272 184

Q4 200 mm 134 337

Annual 929 mm 978 819

Estimate of the reliable draw based on:• 1996 – an average year for rainfall • 2004 – a very dry winter

Usage: L/day 100Roof area: sq m 100

Storage: L 2000 4000 6000 8000Minimum water stored during the quarter

1996Average summer

1996Average winter

2004Dry winter

Days pa without water19962004

Usage: L/day 100Roof area: sq m 100

Storage: L 2000 4000 6000 8000Minimum water stored during the quarter

1996Average summer 5% 52% 68% 75%

1996Average winter 0% 20% 47% 60%

2004Dry winter 0% 0% 0% 9%

Days pa without water1996 25 0 0 02004 57 36 15 0

0 20 40 60 80 100 120 140 160 180 2000

50

100

150

200

250

300

Avg Sum 6000L

Avg Sum 2000L

Roof Area (sq m)

Relia

ble

Dra

w (L

/d)

0 20 40 60 80 100 120 140 160 180 2000

50

100

150

200

250

300Avg Sum 6000L

Avg Win 6000L

Dry Win 6000L

Roof Area (sq m)

Relia

ble

Dra

w (L

/d)

0 20 40 60 80 100 120 140 160 180 2000

50

100

150

200

250

300 Avg Sum 6000L

Avg Sum 2000L

Avg Win 2000L

Dry Win 2000L

Roof Area (sq m)

Relia

ble

Dra

w (L

/d)

Collection equipment

Best value

Style Material Indicative cost - $/kL (2,000 to 5,000L)

1 Round Poly $220

2 Round Steel $320

3 Slimline Poly $400

4 Underdeck Poly $550

5 Slimline Steel $600

6 Underground

Poly $700 plus excavation

Rainwater tank types and costs

OVERFLOWFIRST FLUSH

FINE SCREEN

20 mm dia40 mm dia50 mm dia

FLAP

External self priming pump with controller mounted above the motor.

Submersible pump with external controller – changeover unit

Surface water

Banksia Robur

Conclusion

Rainwater tank installation guidelines:1. Determine your daily need for rainwater.2. Determine the size of your available roof

catchment area.3. A 2000 L tank will provide 50 to 100 L/day from

a 100 sq m or larger roof.4. A 6000 L tank or larger is necessary for

supplying a washing machine or something similar. If the roof catchment area is greater than 200 sq m then the tank is less likely to empty out during dry periods .

0 20 40 60 80 100 120 140 160 180 2000

50

100

150

200

250

300Avg Sum 6000LAvg Win 6000LDry Win 6000LAvg Sum 2000LAvg Win 2000LDry Win 2000LRoof Area (sq m)

Relia

ble

Dra

w (L

/d)

Oatley Flora and Fauna Society27th October 2014

Rainwater Harvesting in OatleyJim Vickery