Rainfall runoff from shed and house roofs can be a reliable, efficient water source that is easily overlooked. Roofs are high yielding and can turn even minor rainfall events into a useful supply of good quality water. Such supplies are ideal for stock and domestic consumption or for use in spraying equipment.
The yield from a roof is dependent upon the area of the roof and the rainfall received, however not all of this is always captured as at times the tank may overflow.
To calculate the volume of rainfall that can be collected from roof area the following formula is used: Volume of water (litres) = Annual average rainfall (mm) x Roof area (m²) x 0.95
*Note: for a rectangular roof the area is the length (m) x width (m)
For example: A shed with the dimensions 15m x 9m has a roof area of 135m² and an annual rainfall of 400 mm will yield 51,300 litres/year (400mm x 135m² x 0.95).
|
Roof catchment area (m2) |
||||||||
|
Annual Rainfall |
50m2 |
100m2 |
150m2 |
200m2 |
300m2 |
500m2 |
1000m2 |
2000m2 |
|
300 mm |
14,250L |
28,500L |
42,750L |
57,000L |
85,500L |
142,500L |
285,000L |
570,000L |
|
400 mm |
19,000L |
38,000L |
57,000L |
76,000L |
114,000L |
190,000L |
380,000L |
760,000L |
|
500 mm |
23,750L |
47,500L |
71,250L |
95,000L |
142,500L |
237,500L |
475,000L |
950,000L |
|
600 mm |
28,500L |
57,000L |
85,500L |
114,000L |
171,000L |
285,000L |
570,000L |
1,140,000L |
|
700 mm |
33,250L |
66,500L |
99,750L |
133,000L |
199,500L |
332,500L |
665,000L |
1,330,000L |
|
800 mm |
38,000L |
76,000L |
114,000L |
152,000L |
228,000L |
380,000L |
760,000L |
1,520,000L |
Source: Managing Farm Water Supplies (2011) Victoria Government Department of Primary Industries
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