In general, turf grasses need about 3/4″—1″ of water per week to maintain green color and active growth. However, during certain times during the summer when high temperatures are the norm, you should allow lawns to naturally slow down in growth during those extreme conditions.
You may let the lawn go almost completely dormant in hot weather. Many factors such as the soil and weather all have a role in the lawn’s water needs. Here are a few guidelines to follow:
Decide Before Hand
Decide before summer heat and drought conditions arrive, to either water lawns consistently as needed throughout the season, or let lawns go dormant as conditions turn hot and dry. Do not rotate back and forth. In other words, don’t let the grass turn totally brown, then apply enough water to green it up, then let the grass go dormant again. Breaking the lawns dormancy actually drains large amounts of food reserves from the plant.
When is it Time to Water
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.
Watch for foot printing, or footprints remaining on the lawn after walking across it (instead of leaf blades bouncing back up). Grasses also tend to turn darker in color as they go under drought stress. Sampling the root zone soil could be another option.
Water as Infrequently as Possible
Thoroughly water when you do water so moisture soaks down to 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, or when summer patch disease is a problem (see Lawn Diseases). Otherwise, avoid frequent watering that promote shallower root systems
and weeds (e.g., crabgrass).