Catchment Area
The catchment area is in most cases the surface of a roof. To estimate how much water can be collected, the area of the roof in plan and the yearly rainfall needs to be known.
As a rule; one millimetre of rainfall of one square meter of impermeable roof (tiles, corrugated iron etc.) will give about 0.8 litre of water, evaporation and minor losses taken into account.
| Example: If the roof measures 5 m x 8 m in plan and the average rainfall in dry years is 750 mm, the amount of rainwater that can be collected in a year is equal to: 5 x 8 x 750 x 0.8 = 24’000 litres. Approximate daily amount of water is 24,000: 365 = 66 litres. The users are able to compare whether this source is appropriate, whether additional catchment areas are required to increase the source or whether the rainwater will strictly be used for consumption only. |
