When I was testing the soil, grass roots in the good areas went down at least 4 inches. I'm inland in So Calif and we got less than 4 inches of rain last year. Where the grass is established, I seldom have to water more than once every 7-10 days. Over the years, I have watched to see which grass dies and which will go without water, and tried to expand the more drought tolerant. Seat of the pants method, but it works for me.