Conserve water by knowing when to water
The best time to water a lawn is from 6 to 8 a.m. During this time, the water pressure is highest, disruption of the water pattern from wind is low, and water lost to the atmosphere by evaporation is negligible. Watering early in the morning also has the advantage of reducing the chance of turf diseases that require extended periods of leaf moisture. Avoid irrigation during midday.
Difficult-to-wet areas such as slopes, thatched turf and hard soils may benefit from application of a low-flow sprayhead to improve surface penetration of water.
Water only when the plant tells you to. Become familiar with areas of the lawn that wilt first — bluish-purple leaves, rolled leaves, foot printing. Water within a day of observing these symptoms. Soil moisture sensors working with your irrigation system, can save up to 40% on your water usage.
Some areas of a lawn usually wilt before others. These areas, called “hot spots,” may be caused by hard soils that take up water slowly, slopes, southern exposures and warmer areas next to drives and walks. Lawns that have unusual shapes also may require some hand-watering to avoid unnecessary watering of paved surfaces, mulched beds and buildings. Dripperlines that have a 12″ or 18″emitter spacing and supply water at a slow rate would be useful in these areas.
(from University of Missouri Extension, 4-2010)