Sydney’s average rainfall is around 1175 mm. a year. Of course, rainfall patterns vary across the large metropolitan area. The pattern is for an average of around 470 mm. to fall between July and December, with some 705 mm. falling from January to June.
Here’s how to calculate how much water you can collect from your roof. Take the number of square metres of roof, multiply by the number of millimetres of rainfall, to give the number of litres. e.g. If you have 150 square metres of roof, and the average Sydney rainfall is 1175 mm, then you could collect over 176,000 litres a year. A 10mm rainfall would yield 1500 litres! In both cases, it’s safest to subtract 10% to allow for absorbtion, evaporation etc.
For your information, here is the official Sydney monthly average rainfall graph, together with the average number of rain days, supplied by the Bureau of Meteorology.
If you live in Sydney (or elsewhere in NSW), we’d like to help you with your water tank requirements. Learn more at our Sydney Water Tanks page.