It’s best to water in early morning, very early, like 5 a.m. This gives the lawn an opportunity to dry before nightfall, a time when many types of fungus are most active. This is also usually a non-peak time for most communities’ water supply. It’s also much better to water early only a couple of times a week than to water lightly more often. Deep soaking encourages deep root growth, whereas light watering encourages the roots to stay close to the surface of the soil, making your lawn more susceptible to heat and drought.
Another thing to keep in mind is that an actively growing lawn will require about 1 to 1.5 inches of water per week. This, of course, will depend on your soil type.