Darrel sent in a note on the Rain Harvest Calculator that he has developed and made available free of charge on his website. Its a dandy.
Its a very good Rain Harvest tool that provides a lot of flexibility — you have control over all of the following:
- Location — specify your location and the calculator looks up the average monthly rainfall.
- Collection area
- Collection efficiency
- Water usage by month
- Water storage available
- Supplementary water available by month
- Specify years with less or more than average rainfall