In this month's newsletter, Howard said...
Howard Garrett wrote:
One application of water every 5 â€“ 7 days is adequate during the Summer. Sandy soils may require a little more frequency. During the winter, no water is required if your soil is frozen and once every other week in the South.
You can over water a lawn, so allow the soil to dry out between waterings. This encourages the plants to grow roots deeper into the soil, making them healthier and more drought tolerant.
Wait for the lawn to tell you it needs water. Foot prints and lawnmower tracks that do not bounce back are signs that your lawn needs water.
When the grass is dormant, you can apply as little as 1 inch of water each month. This amount of water will help keep the lawn alive, but it will not stimulate the lawn to break dormancy.
Some of this seems contradictory to me. To simplify, I always suggest watering once a month in the cool months and increasing the frequency up to once a week in the hottest heat of summer. There are some situations where you should probably water once every 5 days in the summer. Those would be where you have a sandy rubble soil such as they have from about Junction, TX over to about Palm Springs, CA and up to Green River, UT. Evaporation of water from the soil is affected by altitude, humidity, shade, clouds, soil type, grass type, mowing height, soil fungal population, and some other factors which don't come to mind.
So I agree with 1 inch per month in the cool months, but I would do that all at one time if you don't get enough rain to supply that. If your soil surface is still damp from, well, anything, don't water until it dries out. The reason for winter watering is to keep the soil microbes happy. Even though soil temps might be lower than 50 degrees F, the microbes are getting the soil ready for spring.