The best lawns need 2.5cm / 1in of water per week. Keep track of how much water your lawn is getting by setting out a small food tin to collect rain water and irrigation. There is no need to water your lawn once 2.5cm / 1in has been collected in the tin.
Established lawns can endure 4 - 6 weeks without water without suffering long term damage. Don't worry if your lawn turns brown during dry periods. It is simply dormant and will recover with irrigation.
Ensure the placement of your sprinkler waters your lawn, not your driveway or the street.
Make sure the water you use for your lawn is absorbed. Try 20-minute intervals to allow for maximum absorption.
Even if the surface soil is dry, there may still be moisture further down where the roots are. Use a soil probe (such as a screwdriver) to check moisture levels. If you can easily push the probe 10 - 15cm / 5 - 6in into the soil, you don't need to water.