Et or evaporation transpiration rate is the amount of water loss experienced by plants. The ET Rate is the amount of water needed to be replaced, each plant or crop is assigned a percent (K Factor) of that rate based on plant need.

As The Chart Below Shows, with an ET Rate of  1 inch for the week you would
have to water a lawn ( 60%of ET )  or 72 minutes weekly for rotor sprinklers, fixed head sprinklers would need  to water  24 minutes, assuming the precipitation rate for fixed heads is (1.50PR) and rotors (.50PR)

During this same week shrubs ( 40% of ET ) would  need 48 minutes weekly and drought tolerant or low water use plants ( 20% of ET )  would run 24 minutes.
using rotors. Fixed heads would run 16 minutes for water loving shrubs and 8 minutes for drought tolerant plants.

ET Charts For 47' North Zone 14-16  San Francisco Bay Area

Rotor Run Time Based on Evapo Transpiration

Rotor Sprinkler Head A rotor or impact puts out approximately.05Fixed Head Sprinkler inches precipitation (.50PR) in a hour, it usually has a fine stream and rotates. Fixed heads have a large range of precipitation rates up to about 1.5 or 1.7PR. The distance they throw will impact volume. As a general rule do not exceed 7 minutes on run time to avoid soil saturation and run off.


How Long Do I Water ? To The Point Of Lushness, Not Excess Growth. Enough Water To Produce About A ¼ Of Inch Growth A Week On A Blade Of Grass.
Schedule Your Own

When Do I Water? More Often When It Is Hot, Less When It Is Not.Early morning watering is best, several hours before sunrise. There is less wind which allows for
absorption before evaporation. How Long Does That Mean

Gas powered garden tools emit 5% of the nation’s air pollution.

The average homeowner spends 40 hours/year, the equivalent
to one-week vacation, mowing the lawn.

30% to 60% of urban freshwater is used for watering lawns (depending on locale).

A 1,000 square foot lawn requires 10,000 gallons of water per summer
to maintain a “Green” look. (US. News and World Report, 10/28/96)

80,090,000 pounds of synthetic pesticides are used on US. Lawns each year.

When pesticides are regularly applied, 60-90% of earthworms are killed.
Earthworms are invaluable for soil health. (PA Department of Agriculture)

Over 100 million tons of fertilizers are applied to residential lawns and gardens annually. (Audubon)

Redesigning the American Lawn by Herber Bormann. Diana
Salmon, Garden Geballe, Yale University Press, 1993.