Design Your Perfect Sprinkler System — Free AI Irrigation Planner

Everything downstream depends on these two numbers. To find flow rate, time how long a five-gallon bucket takes to fill from an outdoor spigot opened fully, then convert to gallons per minute. To find static pressure, attach an inexpensive threaded pressure gauge to the same spigot with everything else in the house off.

Typical residential supply lands somewhere around 8 to 15 GPM and 40 to 70 PSI. Design each zone to use no more than about 75 percent of your available GPM to leave headroom for friction loss in the pipe. This single constraint is what determines how many heads a zone can support, and ignoring it is the reason so many systems have heads that dribble instead of spray.

A zone should contain only heads of the same type with matched precipitation rates. Never mix rotors and fixed spray heads on one zone: spray heads apply water roughly three times faster than rotors, so any run time correct for one badly over-waters or under-waters the other.

Beyond that, separate lawn from garden beds, sun from shade, and slopes from flat ground. A south-facing strip along a driveway can need nearly twice the water of a shaded north-side lawn. Grouping them together guarantees that one is drowning while the other is drought-stressed, no matter how you set the controller.

Sprinklers apply far more water close to the head than at the edge of their throw. The standard professional answer is head-to-head coverage: space heads so each one throws all the way to the next. That means a rotor with a 30-foot radius sits about 30 feet from its neighbor, not 60.

It feels wasteful and it is not — it is what produces even coverage instead of dry rings between heads. Place heads at corners first, then along the edges, then fill the interior in a triangular pattern for the best uniformity. In windy sites, tighten spacing to roughly 50 to 55 percent of diameter.

Standard spray nozzles apply water at a fixed rate per degree of arc, which means a 90-degree corner nozzle applies four times as much water per square foot as a 360-degree nozzle running the same time. Either use matched-precipitation-rate nozzles, or account for it in your zoning.

Choose by geometry: fixed spray heads for areas under about 15 feet across, gear-driven rotors for larger open lawn, and rotary nozzles for mid-size areas or slopes where their low precipitation rate reduces runoff. For beds, borders and foundation plantings, drip line or micro-emitters deliver water at the root zone and use dramatically less water than any spray head.

Undersized pipe silently eats pressure. As a rough guide, three-quarter-inch lateral pipe handles up to roughly 10 GPM and one-inch up to roughly 16 GPM at acceptable friction loss. Use a backflow preventer — it is required by code nearly everywhere and it protects your drinking water. Bury laterals 8 to 12 inches deep, deeper where winters are hard, and install drain points if you need to blow the system out each fall.

Then program for infrequent deep soaking rather than daily sprinkles: roughly one to one and a half inches per week for cool-season lawn, delivered in two or three sessions. Run early morning, between about 4am and 8am, when wind is lowest and evaporation is minimal. On clay or slopes, use cycle-and-soak, where three ten-minute runs separated by an hour beat one thirty-minute run that mostly becomes runoff. A rain sensor pays for itself quickly and is also required by code in many jurisdictions.