Welcome to my rainwater calculators. Living in South Australia - the driest state of the driest continent - water conservation is very important. With the River Murray drying up and El Niño events changing rainfall patterns, we need to do everything that we can to ease the burden on the water infrastructure.
Rainwater harvesting - collecting the rainwater from our roof and storing it in a tank or tanks allows us to make best use of what rain does fall.
I have two calculators for your enjoyment. Calculator 1 calculates the actual volume of rainwater that you can collect from your roof based on its square area and your average annual rainfall. Calculator 2 produces a chart of rainfall against water collected.
New! I have just released a new version of RainCalc, written in Java. This can be used on any machine with a Java Runtime Environment and graphical user interface. Please see this page for availability and further details.
Need help with rainwater calculations or advice on harvesting? Would you like a customised version of these very popular calculators for your own site? Just send a mail outlining your requirements to matt@kbc.net.au. Both hosted and stand-alone calculation solutions are available. Please note that due to the volume of queries received, we are no longer able to offer free advice on this subject.
Australian visitors should be aware that I have geo-referenced historical rainfall data purchased from the Bureau of Meteorology, so am able to perform calculations on your behalf, if you do not know the rainfall of the place in question.
If you need to pump, filter, treat or control harvested rainwater, please contact Waterflow Control Pty Limited for assistance.
Unlike most tank manufacturers, who size rainwater tanks based on estimated usage of water, I prefer to use the rule-of-thumb method of calculating the potential amount of water that can be harvested and stored. By using the average rainfall volume as the nominal volume of the tank(s), assuming constant draw-off, the tanks will never fill or overflow. In years with higher than average rainfall, there is the opportunity to "stock up" on this valuable resource.
This calculator creates a chart ready for printing, giving amount of rainfall and the actual volume of water that you will collect, barring leaks and evaporation.
This should print out correctly on A4 paper - you may need to adjust page margins on your browser. Large print versions may print out over two or more pages.
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