Do I need a pressure reducing valve, and what does it do?

The 2024 International Plumbing Code (IPC) sets the rule in Section 604.8: "Where water pressure within a building exceeds 80 psi (552 kPa) static, an approved water pressure-reducing valve ... with strainer shall be installed to reduce the pressure in the building water distribution piping to not greater than 80 psi (552 kPa) static." There's one exception: lines serving only hose bibbs and outside hydrants can stay at street pressure.

Phoenix says the same thing in its own design standards. The city's 2021 Design Standards Manual for Water and Wastewater Systems says that where local static pressure exceeds 80 psi, "a private pressure regulating or reducing valve shall be required on the customer side of the service meter." The city's customer service page adds that "Phoenix does not regulate the water pressure beyond the meter on the customer's side," and that private pressure regulators are the owner's responsibility.

So the city delivers the water and the pressure, and you control what happens after the meter. If that pressure is over 80, the valve is on you.

### Why "static" matters

Static pressure is the pressure with every fixture off. It's the number the code cares about. Flow pressure is what's left while water is running, and it's always lower. A gauge reading of 90 psi with everything off means you need a PRV, even if the shower feels fine.

### What about the 120 psi figure?

You may see 120 psi on Phoenix's customer service page. That page is not consistent: one section says a regulator is required so pressure doesn't exceed 120 psi, and another section says 80 psi. The city's design manual and the adopted plumbing code both say 80. Use 80.

A PRV is a spring-loaded valve. Inside, a diaphragm and spring balance against the water on the outlet side. When pressure downstream drops because you open a faucet, the valve opens to let more water through. When pressure climbs back to the set point, it closes down. The EPA's WaterSense sheet describes the most common type, a direct-acting valve, as "a globe-type body with a spring-loaded, heat-resistant diaphragm" that acts on a spring.

The result is a steady pressure indoors no matter what the street is doing. That matters in Phoenix, where the city's design manual says pressure zones run "between 50 to 100 psi" static and "operating pressure fluctuations are normal." Our page on why water pressure is different in different parts of Phoenix explains those zones.

### What pressure to set it at

WaterSense recommends incoming pressure "between 45 and 60 psi to ensure efficient use of water and proper system function," and says to set a PRV in that range. That's a sensible target for most homes and small buildings. Commercial buildings with tall risers or flushometer valves may need a different design, and the IPC's flow pressure table sets minimums at the fixture: 20 psi for a tank toilet, 20 for a pressure-balance shower valve and 35 to 45 for flushometer valves.

### When street pressure swings

Street pressure isn't a fixed number. Phoenix's design manual notes that "the public water system can fluctuate 20 psi higher or lower than the average system pressure." The city's customer page adds that demand "during peak times and during times of little demand" can shift pressure. So a building that reads 75 psi at one hour can top 80 at another. The IPC tells designers to plan for the swing from the other side too: where street pressures fluctuate, Section 604.6 says the system "shall be designed for the minimum pressure available." A PRV handles the high side, so the house sees the same pressure either way.

### The code's other PRV rules

The IPC adds three design rules:

• It needs a strainer, to catch grit before it reaches the valve seat.
• It must fail open. Section 604.8.1 says the valve "shall be designed to remain open to permit uninterrupted water flow in case of valve failure." So a dead PRV usually lets high pressure through instead of shutting your water off.
• It must be serviceable. Parts and strainers have to come out "without breaking a pipeline."

WaterSense puts it simply: high pressure "can damage plumbing piping, fixtures, and appliances, and can lead to increased water consumption, premature equipment failure, and risk of leaks." Phoenix's customer page says pressure over 80 psi "can damage your water pipes and appliances."

In practice that can show up as:

• Toilets that run or refill on their own because fill valves can't hold back the pressure.
• Dripping faucets and hose bibbs that wear out early.
• Banging pipes when a valve snaps shut. The IPC requires water hammer arrestors where quick-closing valves are used.
• Leaking supply hoses on washers, dishwashers and ice makers.
• A water heater relief valve that drips. See why a water heater pressure relief valve leaks.

Our page on what your home water pressure should be covers the ideal range in more detail.

The answer starts with a gauge. Test first, then look for the valve.

1. 1Test the pressure. Screw a pressure gauge onto a hose bibb near where the water enters, or onto the washer's cold water connection. With every fixture off, open the valve fully and read it. WaterSense gives the same test.
2. 2Read the number. Over 80 psi static and you need a working PRV. Between 45 and 60 is the sweet spot.
3. 3Look for the valve. A PRV is usually a bell-shaped brass valve on the main line near where it enters the house, often after the main shutoff. Some sit in a box near the meter.
4. 4If you have one and the pressure is still high, it may be failing or set too high. Our page on the signs a pressure reducing valve is going bad walks through that.

### Adding a PRV means adding expansion control

Here's the catch most people don't hear about. A PRV creates a closed system, so the water heater has nowhere to push the extra volume when water heats and expands. IPC 607.3 says that where a storage water heater's cold supply passes through a check valve, a PRV or a backflow preventer, "a thermal expansion control device shall be connected to the water heater cold water supply pipe." WaterSense flags the same issue. Plan on an expansion tank when you add a PRV to a home with a tank water heater.

WaterSense advises picking a regulator whose operating pressures fall in the middle of its rated range, "not based on the size of the pipe." Check with your city about a permit before the work. HQ Plumbing and Air can test your pressure, replace or install a PRV and add the expansion tank, with free estimates and upfront pricing.