The first variable to determining how long to run your sprinklers is seasonal; the second is sprinkler output. In warmer months, or peak growing season, water for approximately 20-30 minutes a day, every three to five days. Ideally your grass wants 3/4 of an inch to 1 inch of water. In the cooler, slower growing seasons, 10-15 minutes, two to three times per week. If you use automatic sprinklers, be sure to adjust them seasonally.