Knowing how long to water each zone depends upon your grass type, your sprinkler output and the type of soil you have. Some warm-season grasses are better adapted to hot climates and need less water. On average, most lawns require about 1 inch of water per week. If you know how much water your sprinkler puts out in one hour, you can make a better determination of how long you need to water each zone. Lastly, keep in mind that water will run quicker through sandy soils, while clay soils will hold onto the moisture longer.