Use this formula to calculate the square footage of landscape to be irrigated:

LA= GW (ETxPFx0.62) 

LA = Landscaped area 

GW = Estimated Grey Water (gallons per week) 

ET = Evapotranspiration (inches per week)* 

PF = Plant Factor 

0.62 = (inches of ET to gallons per week)

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EXAMPLE:

LA= 1120 ( 120gx7 days = 840 g. per wk) divided by 2x.8x.062

Landscaped area = 1120 square feet. 

*Evapotranspiration is the amount of water lost through evaporation from the soil and transpiration from the plant. This varies depending on location.