The water requirements of a lawn can vary depending on grass species, soil texture, climate and desired level of aesthetics and maintenance. Turf generally needs about one inch of water a week during the growing season to stay green and actively growing. Drought resistant varieties of cool season grasses are available and many warm season grasses can survive with much less than one inch of water per week. As a rule, the healthiest turf is on the thirsty side which encourages root growth as they seek moisture deeper in the ground.
Water is mainly obtained through rain but can be supplemented with lawn sprinklers or an irrigation system. Domestic water supply comes from a public source (at a cost), or a well on your property (free). Recently water supply has been of great concern, with many municipalities imposing water restrictions during times of drought. In extreme cases a lawn may have to 'brown out' and go dormant until the rains return. Our expectations of what a healthy lawn should look like may need to change in the coming years as water becomes more of a scarcity. A prudent lawn care program will help a lawn get through a drought.
A lawn can be watered with a moveable sprinkler or an underground irrigation system. In either case, they require spray overlap for even coverage. Typical lawn sprinklers are inexpensive and must be moved throughout the lawn. Automatic sprinkler systems provide excellent coverage and if used properly, are the most efficient form of supplemental watering. They run on a computerized time-clock that is fully customizable to individual needs.
Water should be applied deep and infrequently to simulate natural weather patterns. Long intervals between watering encourage the grass to develop deep, strong root systems which results in increased drought tolerance. Shallow and frequent waterings lead to shallow-rooted grass and a weaker overall plant. One or two deep waterings per week are better than watering a little every day.
The ideal time to water the grass is in the hours between 3:00 AM and 6:00 AM. If this can't be done, water as early as possible before the heat of the day. Watering in the evening is acceptable as a last resort, but this can lead to conditions which promote disease. Watering in the middle of the day will cool the turf, but most of the water will be lost to evaporation.