How Much Rain Does My Area Get For Me to Collect
The chart below shows the average rainfall received in 2005 and works out how much water the average roof of 250m2 surface area would catch. It really does show you how much water a standard house roof catches in average rainfall. You can also use this information in determining what size tank/s you will buy.
Average Rainfall and Litres of Water Collected by the Average Australian Roof
Average Rainfall Chart provided by the Australian Bureau of Meteorology 2006
Roof Catchment Area
Because of their large surface area, roofs will catch a significant amount of water. The roof catchment area for single storey homes is usually greater than the floor area of the building if there are eaves.
As a guide to collection capacity, consider that each 1mm of rain = 1 Litre (L) of water per square metre (m2) of roof area, then allow a 15% wastage factor.
Another rule of thumb is that the smaller the catchment area the larger the tank should be because when it rains there is a need to capture as much as possible of the run-off.