Factors such as the soil, weather, and management practices all have a role in water needs of lawns. Do not rotate back and forth. In other words, don't let the grass turn totally brown, apply enough water to green it up, and then let the grass go dormant again, as breaking dormancy actually drains large amounts of food reserves from the plant. The first few warm days of summer does not automatically mean to water lawns. In fact, allowing lawns to start to go under mild drought stress actually increases rooting.
Grasses also tend to turn darker in color as they go under drought stress.
Sampling the root zone soil could be another option. In general, water as infrequently as possible. Water thoroughly so moisture gets down to the depth of the roots. Exceptions to this general rule would be for newly seeded lawns where the surface needs to stay moist, newly sodded lawns that have not yet rooted into the soil of the site, or when summer patch disease is a problem. Given a choice, water early in the day when lawns are normally wet from dew.