Water smarter: drip irrigation and watering well

Where the water goes

Water is the one input a garden can't do without, and the one we waste most easily. The EPA's WaterSense program reports that outdoor watering averages more than 30% of household water use, and up to 60% in dry regions. It estimates that up to half of outdoor water is lost to wind, evaporation, and runoff from inefficient irrigation, and that a poorly maintained sprinkler system can waste up to 25,000 gallons a year.

Drip versus sprinklers

Drip irrigation delivers water slowly and directly to the roots, as WaterSense puts it, instead of throwing it into the air. Washington State University Extension estimates sprinklers at about 70% efficient and drip at 90 to 95%. Utah State University Extension is a little more conservative: up to 90% for a well-designed drip system. Either way, the difference is large.

Build a simple drip system

A home drip system has only a few parts, and each one matters. Utah State and Washington State extension guides describe them:

• Backflow preventer: protects your drinking water supply, and many towns require one.
• Pressure regulator: drip runs at about 10 to 30 psi, while household pressure is often 40 to 100, so you need to bring it down.
• Filter: Washington State calls it the most important part of the system. Its openings must be smaller than the emitter holes; Utah State suggests 120 to 200 mesh, checked monthly in the growing season.
• Tubing and emitters: emitters are usually rated from 0.2 to 4 gallons per hour. Pressure-compensating emitters keep the flow even on slopes, and turbulent-flow emitters clog less.

How much, and when

University of Minnesota Extension gives a useful starting point: vegetable gardens need about an inch of water a week, rain included. Soil changes that. Sandy soil may need about half an inch twice a week, while clay or rich loam can go once a week.

The same guidance says to water deeply and less often, so roots grow down after the water, and to water in the morning. Leaves that stay wet, especially overnight, invite disease. If plants are wilting, though, water them right away.

Mulch does half the work

The cheapest irrigation upgrade is mulch. Colorado State University Extension notes that mulch cuts surface evaporation and can reduce how much a vegetable garden needs watering by around 50%. University of Minnesota Extension recommends 2 to 3 inches of organic mulch.

Let the controller think

If you have an automatic system, a smarter controller helps. WaterSense labeled controllers come in two kinds: ones that adjust to the weather, and ones that use a soil moisture sensor to skip watering when it isn't needed. Both are independently certified. The EPA estimates that replacing a clock timer with a WaterSense labeled controller can save an average home up to 15,000 gallons a year.