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.
For your information, here is the official Bureau of Meteorology map showing average annual rainfall (in mm) of Sydney and areas throughout New South Wales, as well as a chart breaking down Sydney’s average rainfall by month.
How To Harvest Your Rainwater (and calculate your savings)
Throughout the country, water truly is the most precious resource we have, and it’s for that reason that so many clever Australians are setting up simple rainwater harvesting systems at their residences.
In these systems, roof guttering collects water runoff and directs it to water tanks. From that point, the stored water can be used to clean, irrigate the garden, wash clothes, or even filtered for potable household use.
Just how much water can you collect from your roof?
Here’s how to calculate it:
Number of square metres of roof X the number of millimetres of rainfall = litres harvested
If you have 150 square metres of roof, and the average Sydney rainfall is 1200 mm per year, then you could collect over 180,000 litres a year (150 x 1200).
A 10mm rainfall would yield 1500 litres! In both cases, it’s safest to subtract 10% to allow for absorbtion, evaporation etc.