2.3 Roof and Gutters:  Tank Sizing

Calculating the rainwater harvesting tank size based on your roof area, rainfall, and consumption

This section is a very powerful spreadsheet where you will enter your roof area that you calculated in the last step, your household water consumption, and rainfall data that we will help you find for your area of the world.  It will graphically allow you to size your tank(s), and simultaneously depict what your tank inventory will be at the end of each month.  Use your total roof area for now.  If you’re collected rainwater turns out to be consistently greater than your consumption each month, consider using fewer roof areas, and then recalculate a tank size.  If you use too much gutter, you’ll simply overflow the tank each month.

DOWNLOAD: Tank Size Calculator Spreadsheet  

Note: The file is an Excel spreadsheet and will require that you have this program installed locally to use it.  Your computer (depending on the browser you use) should give you the option of saving the file locally or simply opening it.  If you accidentally started changing the yellow box values, simply close the spreadsheet without saving and reopen.

Now that you have your tank(s) sized, we will move on to designing and sizing the gutters and downspouts.