Enrichment · Passion Projects · Environment

Water the yard
by what the plants
actually use.

Type the month’s evapotranspiration and list the parts of the yard. The estimator scales the weather by each plant group’s needs and the watering method’s losses, and shows where the water goes.

Estimate the waterWhat you get

The irrigation estimator

The worked example is a made-up back yard in July. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
Each zone’s net need, gallons for the month and inches a week, the total and its cost. It prints as a summary and downloads as a spreadsheet.
Who it is for
Families and students planning a garden, environmental science and agriculture classes, and school garden volunteers.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Look up the month’s ETo where you live.
  2. Estimate the rain that soaks in.
  3. Group the yard into zones by plant water use.
  4. Pick each zone’s plants and watering method.
  5. Set run times from the inches a week.

Estimate the water

How the water need is estimated

Evapotranspiration, plant factor, efficiency.

The worked example: a back yard in JulyPlant need5.76 in7.2 in ETo × 0.8 lawnAfter rain4.96 in− 0.8 in that soaked inLawn gallons6,180× 1,500 sq ft × 0.623 ÷ 0.75Whole yard8,546 galfour zonesThe worked example: a back yard in JulyPlant need5.76 in7.2 in ETo × 0.8 lawnAfter rain4.96 in− 0.8 in that soaked inLawn gallons6,180× 1,500 sq ft × 0.623 ÷ 0.75Whole yard8,546 galfour zones
Weather sets the demand, the plants scale it, and the watering method decides how much extra is lost.

Evapotranspiration

ETo is the water a well-watered reference grass would lose to evaporation and transpiration, measured from weather stations: hot, dry, sunny and windy months push it up. Other plants use a fraction of it, the plant factor: about 0.8 for cool-season lawn, 0.5 for many shrubs and as little as 0.1 to 0.3 for established native plants.

Gallons and losses

One inch of water over one square foot is 0.623 gallons. No system delivers all of it to the roots: wind, overspray and runoff take part, so sprinklers are counted at about 75 percent efficient and drip at about 81. Dividing by efficiency gives what has to leave the tap.

Sources

  1. U.S. Environmental Protection Agency, WaterSense. Water budget approach and outdoor water use (epa.gov/watersense).
  2. University of California Agriculture and Natural Resources. WUCOLS IV: Water Use Classification of Landscape Species (ucanr.edu).
  3. Allen, R. G., et al. (1998). Crop evapotranspiration, FAO Irrigation and Drainage Paper 56. Food and Agriculture Organization (fao.org).
  4. USDA Natural Resources Conservation Service. National Engineering Handbook, Part 652: Irrigation Guide (nrcs.usda.gov).

The worked example is made up. Plant factors and efficiencies are typical values; follow local watering rules. Your entries stay in this browser. Support: team@caveatacademic.com.