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The simple rule is, the larger the roof area connected to the tank, the more water will be collected.
For example, a tank connected to one down pipe on a home with four down pipes will only capture 25% of the rainfall. Increasing the tank size without a greater collection area won’t necessarily increase the amount of water available. Benefits are to be found from early planning of roof design and down pipe positioning relevant to the storage tank.
- Position the tank where two down pipes can easily be interconnected to supply the tank.
- Collecting rainwater from a carport or garage roof, plus a house down pipe will greatly assist collection.
- Consideration of using larger rainwater guttering systems.
- Early planning of tank location will reduce costs.
Imagine the amount of water that could be saved if every home in Australia collected rainwater from its roof.
Using the example of a typical 16 square home, with a roof area of 156 square metres and 800 mm of rainfall, the potential volume of rainwater that could be harvested per year would be:
156 x 0.8 = 124,000 litres
However, this would require all the storm water pipes on the house to be connected to the storage tank, not often very practical.
Aquasource systems are designed to use a single down pipe connection , in this example this would equate to a catchment area of 56 square metres of roof.
56 x 0.8 = 44,800 litres
The average homes yearly water usage is approximately 270,000 litres with 20% (54,000 litres) used to flush the toilet. As a comparison allowing 40 litres per day per person for toilet use, or 14,600 per year, for three people in the home, the total amount of water needed to flush the toilet would equal 43,800 litres.
As long as the rainfall is reasonably well distributed, a high proportion of the water used for toilet flushing will be rainwater supplied from the rainwater storage system.
For example the storage tank on an Aquasource 1500 litre modular system, if full, would allow 10 to 12 operating days without any rain.
142 square metres (16 squares), total roof area = 156 square metres.
All dimensions in metres
Harvesting For Given Rainfall – One Down pipe |
| Yearly Rainfall (mm) |
Square Meters of Roof |
| 40 |
50 |
60 |
70 |
| 1000 |
40,000 |
50,000 |
60,000 |
70,000 |
| 900 |
36,000 |
45,000 |
54,000 |
63,000 |
| 800 |
32,000 |
40,000 |
48,000 |
56,000 |
| 700 |
28,000 |
35000 |
42,000 |
49,000 |
| 600 |
24,000 |
30,000 |
36,000 |
42,000 |
| Note: One cubic metre of water = 1000 litres. |
One square equals 10’ x 10’ or 3m x 3m
A single down pipe can often be complimented with a second storm water down pipe from the carport or garage depending on the physical location of the Aquasource unit. This is allowed for and recommended on systems above 1500 litres.
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