How Much to Water Your Lawn, and How Much Your Rain Already Covers

Most lawns need about 1 inch of water a week during the growing season, rain included.² How much of that you supply depends on where you live: in a typical US ZIP code, normal July rain gives about 0.9 inch a week, but in Los Angeles or Las Vegas it gives almost none, and in Tampa nearly twice the need.⁵

How much water a lawn needs

NC State Extension’s rule of thumb is about 1 inch of water per week while grass is growing.² Purdue Extension puts Indiana lawns at 1 to 1½ inches a week, depending on weather, soil type and slope.¹ On Florida’s sandy soils, UF/IFAS recommends ½ to ¾ inch each time you water, and says that amount should stay the same all year while the number of waterings changes with the season.³

Soil changes how you split the water more than how much the lawn needs. In Washington State University’s lawn watering guide, about 1 inch per watering refills the root zone in silt, loam and clay soils, while sandy soils hold less and do better with about ½ inch at a time, more often.⁸ On clay and slopes, apply it in short rounds so it soaks in rather than running off (see below).

Wet the soil to the depth of the roots, then stop. Purdue warns that light, daily watering encourages shallow roots and crabgrass, and that overwatering can do more damage than drought.¹

How much of that your rain already covers

To see how much is left for the sprinkler, we divided NOAA’s 1991–2020 monthly rainfall normals into weeks for the weather station nearest each of 40,904 US ZIP codes.⁵ In July, the median ZIP code gets 0.90 inch of rain a week. Only one ZIP code in three averages 1 inch or more, and in 42% every summer month from June to August falls short.

These are averages. Real rain arrives in storms, so even where July averages an inch, a dry fortnight can stress a lawn. Use the numbers to set expectations, and let the grass tell you when to water.

How often to water

Water when the lawn asks for it, not on a calendar.

Turf should not be watered by a set schedule.

The first signs of thirst are a blue-green color and footprints that stay visible after you walk across the lawn; Purdue says to water at that point.¹ UF/IFAS adds leaf blades folded in half lengthwise.³ Give the week’s water in one thorough soaking, or in two equal waterings three to four days apart.¹ If you have an automatic system, change its program through the season instead of leaving one setting all summer.^1,3

How long to run your sprinkler

Run time depends entirely on the sprinkler. Purdue’s guide says spray-head systems can apply a large volume in 10 to 15 minutes, rotary heads need 30 to 40 minutes, and most hose-end sprinklers need two to three hours in one spot.¹ To find your own number, set straight-sided cans such as tuna cans in a grid, run the sprinkler for a set time and measure the water in each with a ruler.¹

The best time of day to water

Purdue rates 4 to 8 a.m. as ideal: water pressure is high, wind is low and little is lost to evaporation. Late morning is second best. Midday watering wastes much of the water, and evening watering can raise disease risk.¹ Losses add up:

As much as 50 percent of the water we use outdoors is lost

EPA blames wind, evaporation and runoff from inefficient watering, and notes that outdoor use is more than 30% of household water on average, up to 60% in dry regions.⁴

Slopes, compacted soil and dry spells

On slopes and compacted spots, water until it just starts to run off, let it soak in, and repeat until the soil is wet about 6 inches down.¹ Relieving compaction helps too; see when to aerate your lawn.

If you stop watering in a long drought, the lawn turns brown and goes dormant rather than dying. Purdue says turf can survive four to six weeks dormant; after that, give it 1 to 1½ inches in one thorough watering.¹

Related guideWhen to Overseed Your Lawn: The Last Safe Day Where You Live

Watering new seed, fertilizer and weed preventer

New seed needs light, frequent watering to keep the surface moist, which is the opposite of the routine above; our overseeding guide covers it. Granular fertilizer and crabgrass pre-emergent need watering in after you apply them; see when to fertilize your lawn and when to apply pre-emergent. Not sure whether you have cool- or warm-season grass? Our guide to cool-season vs warm-season grass explains how to tell. The lawn section has the rest of the year’s timing.