Cistern Water for Landscapes
Water captured, as in the example here of Santa Monica, CA, can only go so far in the garden. The water lost through the foliage of a plant is called evapotranspiration or the ET rate. This is based on the growth of unmulched turf grass measured in inches per month or year. The ET rate for the year at Santa Monica is 44 inches but their rainfall is only 14 inches. The water used by plants in a 1000-square foot garden equals about 30,000 gallons per summer. This would require a roof of about 3,500 square feet to capture enough water. Six times the size for each 5,000 gallon tank (that takes up a footprint of 11 feet in diameter on the ground for each tank and seven feet tall) would be a whopping 207+ square feet of ground use.
City water costs about $42.76 per month for the average family in Santa Monica without extravagant water usage. (Including the $500 rebate that Santa Monica provides for each person’s cistern.) The payoff time for the cost of the six 5,000 tanks (no plumbing or pumping) would be 58 years! Is this a worthy investment? Makes groovy ecological sense, but may lack money cents.