There are two good online sources of information that will tell you how long to water your lawn. At the Be Water Wise Calculator you will find an easy to use watering calculator. It will ask for your zip code, type of lawn (cool or warm season), soil type (sandy, loam, clay), type of watering system and a few other questions. The calculator will tell you how many minutes per week to water your lawn each month of the year and the maximum amount of time your sprinklers should run.
You will get the most accurate irrigation schedule if you know and enter how fast your sprinklers apply water into the calculator. To find out how to measure your sprinkler system’s output, click on "Application Rate" in the watering system section of the calculator. Every sprinkler system applies water at a different rate and knowing the rate your system applies water will help the calculator give you the best irrigation schedule.
There is also a free UC publication 8044 Lawn Watering Guide for California which you can download. This publication will tell you how many minutes to water your lawn each week by following a few easy steps.
To save water and have a healthy lawn, you should re-set your sprinkler time clock at least twice a year – in spring and again in fall. Lawn grasses use more water when days are longer (April to September) and less water when days are shorter (October to March). To save more water, turn your controller off when rain is expected or after a good rain (more than ½ inch).
By V. Lazaneo, Urban Horticulture Advisor, Emeritus, UC Cooperative Extension, October 2012