The best efforts may not provide enough water for the lawn. It may not be possible to adequately water a lawn with a lawn sprinkler during the long warm days of summer.
Even clients that have sprinkler systems can have brown areas where the sprinklers do not overlap enough. The key is enough water. The lawn must get 1 ½” of water per week to stay green and growing.
This can be measured by placing a straight sided container in the area I the sprinkler is watering and only moving the sprinkler once 1 ½” of water is in the container.