Quick Answer
A residential sprinkler system pulls pressurized water from the municipal supply, passes it through a backflow preventer (a one-way valve that keeps lawn water out of the drinking line), splits it across electrically-controlled zone valves, and pushes it through underground lateral lines to pop-up heads that distribute water in measured patterns. A controller on a timer decides which zone runs when. The whole system has six failure points and most of them announce themselves before they get expensive.
Detailed Guide
The components, in order of water flow
Water travels through eight named parts between the city main and the lawn. Every irrigation conversation a contractor has uses these terms.
| Order | Component | Function | Common failure |
|---|---|---|---|
| 1 | Point-of-connection (POC) tap | Where the irrigation line splits from the house supply | Leaks at the saddle clamp |
| 2 | Backflow preventer | Stops lawn water (and any fertilizer or pet waste it contacts) from siphoning back into drinking water | Internal seals fail at 8-12 years |
| 3 | Main line | Pressurized pipe from backflow to valve manifold | Frozen split if winterization is skipped |
| 4 | Manifold + zone valves | Electric solenoid valves that open/close each zone | Solenoid diaphragm tears; valve sticks open |
| 5 | Lateral lines | Lower-pressure pipe from valve to the heads in that zone | Crushed by tree roots or shovel strikes |
| 6 | Heads | Pop up under pressure, distribute water | Clogged nozzle, broken riser, blocked by mulch |
| 7 | Controller (clock) | Schedules zone run times | Battery dies; lightning fries the board |
| 8 | Sensors (rain, flow, soil moisture) | Override the schedule when conditions warrant | Rain cup fills with debris and disables system |
Backflow preventer: RPZ vs DCV
The backflow preventer is the most safety-critical and most code-regulated part of the system. Two types are common.
Double Check Valve (DCV). Two spring-loaded check valves in series. Cheaper, smaller, and installable below grade. Approved for low-hazard residential irrigation in most municipalities. Failure mode is silent — a stuck check valve provides no warning.
Reduced Pressure Zone (RPZ). Two checks plus a relief valve that vents to atmosphere if either check fails. Required where any chemical injection (fertilizer, herbicide) is possible, and increasingly required for all new residential irrigation in municipalities that have adopted updated cross-connection codes. Must be installed above grade and tested annually by a certified backflow tester ($75-$150 per test).
The annual RPZ test is non-optional in most cities — the water utility will tag the meter if the test report is not filed.
Zone valves: how the controller turns water on
Each zone has one electric solenoid valve buried in a green plastic box near the manifold. The controller sends 24V AC down a thin wire to the solenoid coil, which lifts a small plunger off a pilot port. That opens the main diaphragm, water flows, and the heads in that zone pop up.
When the cycle ends, the controller cuts power, the plunger drops, the pilot port closes, and water pressure pushes the diaphragm shut. A valve that will not close (zone runs forever) is almost always a torn diaphragm or debris on the seat — a $12 diaphragm kit and 20 minutes.
Heads: four types, four jobs
The nozzle is where the system's water-use efficiency is won or lost. EPA WaterSense data shows nozzle upgrades alone can cut irrigation use by 20-30%.
Spray heads (fixed pop-up). Fan a fixed pattern (90°, 180°, 360°) up to about 15' radius. Best for small, square turf areas. Precipitation rate is high (1.5-2.0 inches per hour) — they put down a lot of water fast.
Rotor heads. A single stream rotates back and forth across an arc, throwing 20-50'. Slower precipitation rate (0.4-0.8 inches per hour) gives soil time to absorb instead of running off. Best for large open turf.
MP Rotator / multi-stream rotary nozzles. Multiple thin streams rotate slowly, matching spray-head radius (8-30') with rotor-grade precipitation rate (~0.4 inches per hour). The current best-practice retrofit for any spray zone on a slope or with runoff.
Drip emitters / inline tubing. Deliver water at the root zone at 0.5-2.0 gallons per hour, per emitter. Required by most municipal codes for any new non-turf landscape (shrub beds, planters). Almost zero evaporation loss.
Controller: smart vs dumb
A traditional controller runs the schedule the homeowner programs and does not adjust for weather. A WaterSense-labeled smart controller pulls local ET (evapotranspiration) data from a weather station or the National Weather Service feed and skips or shortens cycles when the lawn does not need water. EPA estimates a smart controller swap saves 7,600 gallons per home per year on average — about $40-$80 on a metered water bill depending on local rates.
Rain and flow sensors
A rain sensor is a small cup that swells with moisture and opens an electrical contact on the controller's sensor circuit. When the contact is open, the controller skips its next cycle. Required by code in Florida, Texas, Georgia, New Jersey, Minnesota, and a growing list of others.
A flow sensor is a turbine in the main line that reports actual gallons-per-minute to the controller. If a lateral breaks (flow jumps 30%+ above baseline), the controller shuts off the zone and sends an alert. Optional on residential systems but pays for itself the first time a head breaks at 2 AM.
What fails first: a troubleshooting table
| Symptom | Most likely cause | Fix |
|---|---|---|
| Whole zone has low pressure | Clogged main filter at backflow OR partially closed isolation valve | Clean filter screen; verify isolation valves are fully open |
| Brown stripes between heads | Mismatched nozzles within a zone (e.g., 180° head with 360° head) | Replace nozzles so all heads in a zone have matched precipitation rates |
| One head shoots straight up | Cracked or missing nozzle | Replace nozzle (under $5) |
| Valve runs continuously | Torn diaphragm or debris on the seat | Replace diaphragm ($10-$15 kit) |
| Controller dead, display blank | Blown transformer or tripped breaker | Reset breaker; replace 24V transformer ($25-$40) |
| Whole system off after storm | Lightning-damaged controller board | Replace controller |
| Pop-ups stuck down | Mulch or soil packed around the body | Excavate around head, flush riser |
| Rain sensor never resets | Debris in the cup, or expansion disk failed | Clean cup; replace sensor if 8+ years old |
Most of these are owner-fixable with a screwdriver and a $30 visit to the irrigation aisle. Solenoid replacement, controller replacement, and main-line repair are also DIY-eligible. Backflow tests, system winterization with compressed air, and any work upstream of the backflow are licensed-pro work in most states.
When to Hire a Pro
Irrigation has a clear DIY/pro line, and crossing it incorrectly creates either a code violation or a flood.
Hire an irrigation contractor for the initial system design and install — sizing the main line, calculating precipitation rates per zone, and laying out head spacing for head-to-head coverage are math problems that get expensive when guessed. Expect $2,500-$5,000 for a 5-6 zone install on a quarter-acre lot, plus $400-$800 for the permit and backflow inspection.
Hire a licensed backflow tester annually for the RPZ test — most cities require the tester to be certified, and the report must be filed with the water utility. A landscape contractor without the certification cannot legally sign the report.
Hire for winterization in any climate that freezes — the contractor uses a 10-20 CFM compressor to blow lines clear at 50 PSI. A homeowner shop compressor cannot move enough volume to clear a residential system, and a partially-cleared line splits at the first freeze.
DIY-eligible jobs: nozzle swaps, head replacements, solenoid swaps, controller upgrades, rain sensor installs, and adjusting arc and radius on existing heads. Anything upstream of the backflow preventer (including the POC tap on the house supply) is licensed plumber work in every state.