Below find resources links we feel will help you better understand the various elements of rain harvesting.
System Size Calculator A downloadable Excel spreadsheet, the comprehensive calculator estimates the size of the rainwater harvesting system based on the user's inputs. The information in this file is provided as a public service by the Texas Water Development Board, and should be used for estimation purposes only.
Rainfall Runoff Map The map shows the average annual collectable water in 000s of gallons from a 2,000 square-foot roof. A local hill country home with 2,000 square feet of roof area receives about 28,000 gallons of harvestable water per year. The numbered lines on the map are isolines, connecting points of equal average annual runoff (in thousands of gallons).