 |
|
Water
Savings From Urban Water TanksBrisbane |
101,000
litres/ 65% of indoor use/ 56% less stormwater |
Sydney
|
100,000
litres/ 65% of indoor use/ 48% less stormwater |
Perth |
83,000 litres/ 53% of indoor use/ 67% less stormwater |
Melbourne |
80,000
litres/ 51% of indoor use/ 75% less stormwater |
Adelaide |
72
,000 litres/ 46% of indoor use/ 77% less stormwater |
Hobart |
71,000
litres/ 45% of indoor use/ 75% less stormwater |
Estimated maximum rainwater collection efficiency from the roof of an average home is 80% and therefore the maximum possible reduction in stormwater discharge is 80%.
In Sydney and Brisbane, a 10,000 litre capacity rainwater tank will yield about 80% of indoor water use with about a 60% reduction in stormwater. In the other cities a larger rainwater tank would provide a very small additional yield.
Storing rainwater for garden watering is a highly inefficient use of a rainwater tank and should never be a primary use if the objective is to maximise water yield.
Australia has 5 million free standing family homes. If 5% of homes install a rainwater tank each year, security of urban water supply will be assured by 2014.
BASIS OF ABOVE CALCULATIONS
1. Water Demand Based on average household water consumption for Melbourne.
Total water use for an average household is 240KL/Y comprising:
| Garden | 35% |
| Bathroom | 26% |
| Toilet | 19% |
| Laundry | 15% |
| Kitchen |
4% |
| Drinking | 1% |
65%
or 156KL/Y is used indoors.
- Source: Melbourne Water Resources Strategy
Committee, June 2001, pages 14, 17.
2. Rainfall
The rainwater tank yield calculations were based on daily rainfall as recorded between 1980 - 2001 inclusive at the following sites of the Bureau of Meteorology:
Sydney
Regional Office site 66062
Melbourne Regional Office site 86071
Brisbane Regional Office site 40214 (1980 - 1993)
Brisbane Airport site 40842 (1995 - 2001)
Adelaide Regional Office site 23090
Perth Airport site 9021
Hobart Regional Office site 94029
3. Roof Run-Off
Run-off (litres) = A x (Rainfall - B) x Roof Area, where
A
is the efficiency of collection and a value of 0.8 is used.
B is the loss associated with adsorption and wetting
of surfaces and a value of 2 mm per month (24 mm per year) is used.
- Source: National Environmental Health Forum
Monograph - water series 3: guidance on the use of rainwater tanks,
1998. /http ://enhealth. nphp. gov. au/council/pubs/pdf7rainwtr.
pdf
Roof
area of average home: 175M2
- Source: Melbourne Water Resources Strategy
Committee.Tank draw-down/day: 427 litres (156 000/365).
Amount
of rainfall to produce 427 litres: 3MM (175 X 3 X 0.8)
Total stormwater discharge = (Rainfall -24MM) X
Roof Area
This article is based on a Report by Urban Rainwater Systems.
Click
here to read "Securing
Australia's Urban Water Supply".
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©Enviro-Friendly.com 2002-2012 All information provided in good faith- E&OE
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