The average annual rainfall over the five watersheds of focus is 48.80 inches. The total area of the watersheds is 685 square miles, or 19.1 billion square feet.
To convert to gallons, multiply the average annual rainfall (48.80 inches) by the total area (19.1 billion square feet). Then, multiply this figure by a conversion factor of 0.623. The final result of this calculation is a total of 581 billion gallons.
In a perfect world, Harris County would be able to harvest all of this water. However, this is physically impossible due to the lack of availability of land and willingness of home and business owners to implement rainwater harvesting systems. Assuming just 5% implementation over all residential, commercial, and agricultural areas within the 5 watersheds, there are still 29.05 billion gallons of water available to be harvested over a course of a year. [51]