An in-ground sprinkler system taps the home's water supply at a point of connection, usually through a shutoff and a pressure regulator. Water then passes a backflow preventer, runs through a main supply line to zone valves in a valve box, and reaches the sprinkler heads on secondary lines that hold water only while a zone runs. A controller opens the valves.
The parts, in the order the water reaches them
Colorado State University Extension's irrigation guide lists the basic components of every in-ground system. Here they are in flow order.
1. Point of connection. This is where the supply line taps the home's water supply. The University notes that it is usually in the basement of a typical house, and that the pipe size and water pressure determine how many heads can run at once. Many Arizona homes have no basement, so yours may be elsewhere, such as near the meter or where the line enters the house. A plumber can show you where it is. It is worth knowing before you need it, because it is where you shut the whole system off.
2. Shutoff and drain valves. The University's figure shows a shutoff valve for the outdoor line and a drain valve that empties the outdoor line to the backflow device. A stop-and-waste valve between the supply and the backflow device does this job. Our page on how to winterize a sprinkler system in Arizona explains why it matters.
3. Pressure regulator. A regulator gives uniform, lower pressure for even water delivery. The University says it is typically found just before the point of connection, should be set at 30 to 40 psi for the irrigation system and household water use, and is typically missing in older homes. It adds that sprinkler systems have maintenance problems, and valves may fail to shut off, when pressure is above 80 psi.
4. Backflow prevention device. Local building codes require this to protect the community's water supply. It is typically placed where the water line comes out of the house, and some valves have one built in. The type you must use depends on your local code.
5. Main supply line. This is the line that holds water under pressure throughout the season. It splits in the valve box to give each zone its own valve. The University recommends Schedule 40 PVC for below-ground supply lines and copper for any above-ground pipe.
6. Zone valves. These sit together in the valve box. Each opens for its zone when the controller tells it to.
7. Secondary lines. Beyond each valve, the lines have water only while their zone runs. The University says they are generally flexible black poly pipe, connected with pinch clamps. Pipe size and pressure decide how many heads a zone can carry.
8. Sprinkler heads. Pop-up spray heads suit small to moderate lawn areas. Rotor heads suit larger lawns. The University advises not to mix sprinkler types in a zone, since each delivers water at a different rate.
9. Controller. The timer runs the system from a central location, typically the garage.
Why the backflow preventer is required
A sprinkler line is a pipe full of water that sits in soil, near fertilizer and pesticide, and it is tied to the water you drink. The University's backflow guide explains the risk. A drop in pressure in the main line, from a break or from high demand, can pull contaminants such as fertilizers, pesticides and manure back through the sprinkler heads and pipes into the drinking water supply. The guide calls this back-siphonage and describes it as a serious threat to public health. A pump or injector installed wrongly can also push contaminants back in, which is backpressure.
The University describes the devices commonly used on homes:
- Atmospheric vacuum breaker (AVB). Works by gravity and must be vertical. One is needed for each zone, downstream of the shutoff valve, and it must sit at least 6 inches (check local codes) above all downstream piping and outlets. It only protects against back-siphonage, and the guide says to check with local officials because AVBs may not be legal where you live.
- Pressure vacuum breaker (PVB). One serves the whole system, sits upstream of the control valves, and must be installed at least 12 inches above downstream piping. It is tested yearly by a backflow technician.
- Reduced pressure (RP) assembly. The highest protection, against both back-siphonage and backpressure, needed where contaminants are injected into the system or other hazards exist.
Which one your home needs, who must test it and how often depend on your city. Read the backflow preventer rules for sprinklers in Arizona for the Valley picture. The University adds that a hose-end sprayer attached to a hose bib should have a hose connection vacuum breaker as minimum protection, which our page on what a hose bib vacuum breaker is covers.
Permits, codes and who does what
The University states that all sprinkler systems must comply with local building codes, requiring building permits and inspection, and that permits normally are required for systems that need backflow devices. The design, including the type and placement of the backflow device, is approved during the permit review. Plan on checking with your city's building department before you start.
The tie-in to your water line is plumbing work. Cutting into the supply, adding a backflow assembly and setting a regulator are jobs where a mistake can contaminate the house's water or flood a yard, so they usually belong to a licensed plumber. The rest, such as heads, poly pipe and timer settings, are often done by an irrigation contractor or a careful homeowner.
### Three examples of how the connection shows up in real problems
These are made-up examples to show the reasoning, not real jobs.
Mist clouds around every head. The University says a "mist cloud" around a head is a common symptom of excessive pressure. If a system lacks a regulator, adding one at the point of connection may be the fix. Our page on pressure reducing valves explains when a house needs one, and high water pressure covers the symptoms.
A zone that won't stop. A stuck zone valve keeps the line pressurized. The fast stop is the irrigation isolation valve, and why a sprinkler system won't shut off walks through the causes.
A wet spot with no head nearby. Water is escaping from the main supply line or a secondary line. A buried leak can hide, and how to fix drip irrigation covers small repairs on the drip side. If your water meter runs when everything is off, try a water meter leak test.
Before you dig or add a zone
New zones and new lines are excavation, and Arizona law requires a call to Arizona 811 first. Our page on how to plan landscaping without hurting plumbing lines explains the steps and why the utilities will not mark private irrigation lines.
The Phoenix Water Services household plumbing tips add a habit worth having: know where your main shutoff valve is, and do not shut off water at the meter, which needs a special tool and may make you responsible for meter damage. The same page notes that exposed pipes, especially PVC, are more susceptible to extreme temperatures, which is why an above-ground backflow assembly gets extra care.
HQ Plumbing offers free estimates and upfront pricing, and can check the supply connection and pressure regulator, and replace or install a backflow assembly.