How much?...How Often?
Turf grass roots absorb water from the soil. The amount of irrigation water applied should wet the grass root zone which, for most grasses, is the upper 6 - 8 inches of soil. It is always better to water an established lawn deeply (to wet the root zone) and less frequently than it is to apply a little water on a frequent basis. Light watering promote shallow rooting which reduces the ability of the turf to withstand periods of drought.
Watering 'deeply' will vary depending upon the type of soil in the homeowners's lawn. For instance, heavy clay soils require longer periods of watering than sandy soils to we the depth of the root zone. However, sandy soils also dry out sooner, and they require more frequent water applications than clay soils.
In general, lawns require 1 inch of rainfall or irrigation water per week to adequately wet the root zone and maintain turfgrass quality. (For perspective, it takes 640 gallons of water to apply one inch of water to 1000 sq. ft.)
Wet soils happy lawn