Welcome to Roger's Rainfall, Catchment Area, and Water Program!

When contemplating building a rainwater catchment system, there are a bewildering number of variables to juggle. I created the program below to give you the ability to easily play around with three of these variables. I have crafted this program so that, (unlike many of the other free calculators on the internet today), you can input any two of the relevant variables and have the third one calculated for you. The three variables that I was mostly concerned with are: 1. The annual rainfall that is available at your location or that is required to meet your needs. 2. The catchment area that you have available, are considering building, or that you would need in order to meet your needs. 3. The quantity of water, (measured on an annual basis), that your system would provide, or that you would require to meet your needs. To use the program, simply select the variable that you would like to calculate from the dropdown, choose the type of units that you prefer, fill in the other two fields with values that correspond to your situation, and click calculate.

Please keep in mind that the values produced by this program are hypothetical in nature and do not take into account things such as evaporation losses, droughts, excessive rainfall events, changes in your local climate, temperature, rain shadows, local micro-climates, etc… You should not rely solely on the values produced by this program when you are designing your system. This program is only intended for hypothetical exploration of ‘what if...’ scenarios. If you choose to use the values produced by this program for purposes other than that, you do so at your own risk. Furthermore, the values that this program produces are only averages based on an average annual rainfall. The annual rainfall at a particular location in a particular year may be higher or lower than the values that this program provides or allows you to input. Therefore, do not assume that you can safely rely solely on rainwater catchment to provide the water that you need. This program only allows you to see a hypothetical scenario that would, on average, provide the relevant amount of water. Also, please keep in mind that rainwater collection may or may not be legal where you live. Check with the applicable government agency to ensure that rainwater collection is legal in your area before attempting to build such a system.


What variable would you like this program to calculate for you:

What unit system do you prefer:


For your convenience, here are some relevant water usage statistics for a few regions, (collected in June of 2019), along with some other relevant information:

The average United States resident uses about 32850 gallons or 124350 liters of water per year. [Source]

The average European resident uses about 54750 liters or 14463 gallons of water per year. [Source]

The average Canadian resident uses about 91615 liters or 24202 gallons of water per year. [Source]

The average New Zealand resident uses about 82855 liters or 21888 gallons of water per year. [Source]

The average Australian resident uses about 124100 liters or 32783 gallons of water per year. [Source]

The average Indian resident uses about 33419 liters or 8828 gallons of water per year. [Source]

1 US gallon is about 3.7854 liters.

1 liter is about 0.2641729 US gallons.

1 acre-foot is about 325851.427 US gallons.

1 cubic meter is exactly 1000 liters.

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