Irrigation Systems and Water Efficiency

Match the head type to the area: gear-driven rotors for large turf (25-50 ft throw), fixed spray heads for smaller lawns and beds, bubblers for tree wells, and drip or micro-spray for shrubs and narrow strips.

Space heads head-to-head (100 percent overlap) so each head's throw reaches the base of the adjacent head; spray heads apply less water at the outer radius, so overlap is required for even coverage.

Use matched precipitation rate (MPR) nozzles within a zone so quarter, half, and full-circle heads all apply water at the same depth per hour on one run time.

Never mix rotors and spray heads on the same valve, because they apply water at very different rates and cannot be scheduled together efficiently.

Precipitation rate (inches/hour) = (96.3 x total GPM) / area in square feet; use it to match application to soil intake and avoid runoff.

Convert flow when scheduling: GPM x 60 = GPH; keep zone demand within the water meter's available flow, and split zones that exceed it.

Run fixed spray heads near 30 PSI; high pressure causes misting and fogging that drifts and wastes water, so add pressure regulation when static pressure is high.

Keep design velocity at or below about 5 feet per second and use slow-closing valves to prevent water hammer, which can burst pipe over time.

As pipe diameter decreases for a given flow, velocity and friction (pressure) loss rise sharply, so size pipe to keep distant heads properly pressurized.

A reduced pressure principle (RP) assembly is the highest protection, guarding against both backsiphonage and backpressure, and is required for high-hazard systems such as those injecting fertilizer or chemicals.

A pressure vacuum breaker (PVB) protects against backsiphonage only and must be installed at least 12 inches above the highest downstream head.

An atmospheric vacuum breaker (AVB) is the simplest device, protects against backsiphonage only, must have no valves downstream, and cannot be under continuous pressure.

Backflow devices protect the potable water supply from contamination and are commonly required by local water agencies on irrigation systems.

Automatic valves use a 24-volt AC solenoid energized by the controller; the low voltage is safer and easier to run underground than line voltage.

Weather-based (ET) or smart controllers adjust run times from local weather data, and rain sensors suspend watering after sufficient rainfall.

Use cycle-and-soak (short repeated cycles) on clay soils and slopes so water infiltrates instead of running off.

Under California MWELO (Title 23), estimated water use must stay within the Maximum Applied Water Allowance (MAWA), based on reference ET, landscape area, and an ET adjustment factor.

MWELO restricts overhead spray in strips narrower than about 24 inches; use drip or subsurface irrigation there to avoid overspray and runoff.