Each fixture outlet needs a minimum flow pressure at peak demand, from 8 psi for most sinks to 25 psi or more for flushometer valves. Phoenix supplies at least 40 psi at the meter where the property sits in the right pressure zone. Add a booster below that, and a regulator above 80 psi static.
What pressure does each fixture need?
IPC Table 604.3 lists the required capacity at fixture supply pipe outlets "under conditions of peak demand." It gives both a flow rate and a minimum flow pressure for each fixture. A few of the entries:
| Fixture supply outlet | Flow rate (gpm) | Flow pressure (psi) |
|---|---|---|
| Lavatory, public | 0.4 | 8 |
| Drinking fountain | 0.75 | 8 |
| Sink, service | 3 | 8 |
| Urinal, valve | 12 | 25 |
| Water closet, siphonic, flushometer valve | 25 | 35 |
| Water closet, blow out, flushometer valve | 25 | 45 |
| Shower, balanced-pressure or thermostatic mixing valve | 2.5 | 20 |
The pattern is the point. A flush valve toilet or urinal needs a lot more pressure than a faucet, so flushometer fixtures are the most sensitive to low pressure. The table notes that fixtures not listed follow the manufacturer's installation instructions. For why those flows are not simply added together, see how a commercial water line is sized.
What pressure does Phoenix deliver?
Phoenix Water Services says its roughly 72 pressure zones "operate nominally within a static pressure range between 50 to 100 psi and provides a minimum of 40 psi at the customer's meter, in accordance with the City's Code." There is a catch: "This 40 psi minimum applies only if the property elevation is within the pressure zone elevation range, otherwise the developer/owner is required to install a private booster facility." The same manual notes that "operating pressure fluctuations are normal." Other Valley cities and private water companies have their own figures, so ask your provider for the pressure at your meter.
When is a booster pump required?
When the supply cannot meet the table above. IPC Section 604.7 says: "Wherever water pressure from the street main or other source of supply is insufficient to provide flow pressures at fixture outlets as required under Table 604.3, a water pressure booster system conforming to Section 606.5 shall be installed on the building water supply system." Section 604.6 adds that where street pressure fluctuates, the system "shall be designed for the minimum pressure available." Phoenix's manual points to one cause directly: a property outside the zone's elevation range. Section 606.5.1 allows an elevated tank, a hydropneumatic booster or a booster pump. Our page on booster pumps for low pressure covers the equipment side.
When is a pressure regulator required?
Above 80 psi static. IPC Section 604.8: "Where water pressure within a building exceeds 80 psi (552 kPa) static, an approved water pressure-reducing valve conforming to ASSE 1003 or CSA B356 with strainer shall be installed to reduce the pressure in the building water distribution piping to not greater than 80 psi (552 kPa) static." The exceptions cover service lines to sill cocks and outside hydrants, and main supply risers where pressure is reduced to 80 psi or less at individual fixtures. Phoenix's Water Services manual says the same thing from the utility side: "Where local static water pressure exceeds 80 psi or as per the COP Plumbing Code, a private pressure regulating or reducing valve shall be required on the customer side of the service meter."
That means a building with 100 psi static at the meter needs a regulator, and then the regulated side must still meet the Table 604.3 minimums at the farthest fixture. Where it sits relative to the meter is covered in where the pressure reducing valve goes, and how to tell when a regulator is failing covers the symptoms.
Does Phoenix amend these pressure rules?
Phoenix's amendments to the 2024 IPC list Section 604.4 (flow rates and water consumption) but not 604.3, 604.7, 604.8 or 606.5, so the base text above applies to IPC-based plans. Designs under the Uniform Plumbing Code follow that code's own pressure sections.
What should a business owner do about low or high pressure?
Measure first. A gauge on a hose bib or the main shows static pressure, and a second reading with several fixtures running shows how much drops under load. A big gap between the two can come from pipe sizing, a clogged strainer or a failing regulator. High static pressure means checking whether a regulator is installed and working. A plumber can read both and tell you which fix applies, and why water pressure drops when several fixtures run walks through the common causes.
HQ is licensed and insured and gives free estimates on commercial water pressure problems, with upfront pricing before work starts.