Green grass is a lovely thing.  It's great for picnics and makes a wonderful playing surface for everything from volleyball to croquet.  A good lawn is a deep-rooted lawn that can get through drought and come back strong.

To create a deep rooted lawn, water only when needed, which means during dry spells.  If your area has had at least an hour of rain over the preceding few days, you probably don't need extra water on the lawn.   The only exception to this rule is when you have just seeded an area.  New grass needs daily watering until it is established.

When you have to add water, do it at a time of day when that precious resource will do the most good.  Early morning is best.  Evaporation is minimized and a larger amount of the water will actually get to the plants' roots, making it easier for them to withstand the heat of a July or August day.

By cultivating a deep-rooted, healthy lawn, you can probably even get through periods when watering is very limited or banned all together.  Healthy lawns may brown out and go dormant during such times, but will green up when the rains return.