It depends on your grass, soil and weather, so university extension services give a range rather than one number.
The numbers
1 to 1½ in.
of water per week for most lawns in Indiana, depending on weather, soil type and slope, according to Purdue Extension.
¼ to 1 in.
per week, minus any rainfall, depending on soil type and air temperature, according to University of Minnesota Extension.
Rain counts toward the total. A rain gauge in the yard tells you what actually fell, which is often different from the airport reading a few miles away.
Water deeply, not daily
Purdue recommends putting the week’s water down in one thorough soaking, or two equal applications three to four days apart, rather than light watering every day. Daily light watering, it says, promotes shallow roots, turf that handles drought poorly, and crabgrass.
Soil changes the schedule. Minnesota Extension says sandy soils may need watering two or three times a week with less water each time, while clay soils need it only once a week.
Best time of day
Purdue puts the ideal window at 4 to 8 a.m., when water pressure is usually highest, wind distorts the spray least and little water is lost to evaporation. A controller can run then without anyone getting up.
Measure what your sprinklers put down
Purdue suggests setting shallow, straight-sided containers such as empty tuna cans in a grid around a sprinkler, running it for a set time, and measuring the water in each can with a ruler. It also notes that spray heads can apply a large volume in 10 to 15 minutes, and rotary heads in 30 to 40. Do the can test once per zone and you know how many minutes equal an inch.
Signs the lawn needs water
Purdue describes grass that turns a bluish-green color and footprints that stay in the turf after you walk on it. Wilted turf should be watered without delay.
Letting it go dormant
In a dry summer you can let a lawn go brown and dormant instead of watering it. Purdue says turf can survive four to six weeks dormant without significant thinning, and that after four to six weeks of dry weather a dormant lawn should get 1 to 1½ inches in one thorough watering. That keeps the crowns and roots alive without greening the grass up.
Sources
- Purdue Extension AY-7, Irrigation Practices for Home Lawns (Throssell and Reicher), checked Oct 26, 2026
- University of Minnesota Extension: Water wisely, start in your own backyard, checked Oct 26, 2026
- EPA WaterSense: Outdoors, checked Oct 26, 2026
For more on caring for the grass itself, Really Great Lawn covers lawn care.