Unless your yard is somehow blessed with perfectly timed rainfall throughout the growing season, you'll need to supplement nature's water supply. Here are some tips for watering grass wisely. Water heavily at infrequent intervals. On average, a lawn needs about 1 inch of water per week, from rainfall or irrigation. This will soak the soil to a depth of 4-6 inches, putting water deep into your lawn's root system. Let the lawn dry out completely between waterings. Place small cans around the yard when you water to measure you fast your sprinklers dispense water and to ensure you're covering the entire area. A thorough watering takes a while, however, so be prepared to leave the water running.
For best results, water in the early morning when there is less wind and heat. Cool, calm conditions limit evaporation, allow greater soil penetration, and reduce runoff. Pause when the water puddles or runs off the yard, and let the water soak in before starting again. Most sprinklers and sprinkling systems apply water faster than the lawn can drink it up. Water soaks in at different rates in different soil types. If you have sandy soil, it could take as little as 15 minutes for a half inch of water to soak in. With clay, it could take 10 times longer.