There are a lot of variables that go into calculating water needs. it all starts obviously with the right inputs. Crop coefficients and Precipitation Rates are two, Xeriscape and Native Trees can be as low as 30 to 35. You will have to adjust for each emitter type and soil. Drip, spacing of the emitters and spacing between the lines as well as the GPH all need to be designed based on soil type and zoning or microclimates really prior to install to determine the actual precipitation rate.
