Don't water in the middle of a hot day. Watering when it is cooler allows water to penetrate into the root zone where it can be most helpful to the plant. A good rule-of-thumb is to not water between the hours of 9am and 7pm.
Water deeply. Deep soak your lawn's root zone where the water won't evaporate as quickly and will do the most good for the plant. By using a soil probe (or even a screwdriver), you can determine if your soil is moist in the root zone. If it’s dry then it may need more water. But, if it's moist, don't water!
Don't over water. Excessive watering means that fertilizers and pesticides will move out of the root zone of the plant, rendering them ineffective. What's worse, is that those toxins can then penetrate into the groundwater, impacting water quality and increasing the environmental burden.
Avoid watering on windy or rainy days. Here are some easy sayings to help you remember: “If it's windy, wait a day.” And “If it's rainy, wait a day.” Don't water in adverse weather.
Put soup cans out on your lawn and determine how much time it takes to put 1 inch of water on the ground.
Avoid watering the entire lawn for the few brown or dry patches, investigate and see why it is dry. Do you need to add a sprinkler, or make adjustments to others?
Let your grass grow longer, and train your roots to grow deeper. Letting your grass grow longer means less watering, mowing, and improved root depth (and thus, water-use efficiency). Raise mowing height to 2 1/2 to 3 inches so that the lawn can shade itself.