How to check water pressure

There is no single "normal" house pressure in the International Plumbing Code (IPC). There is a ceiling and a set of floors, and they measure different things. The ceiling is IPC 2021 §604.8: where static pressure inside the building exceeds 80 psi, an approved pressure-reducing valve (PRV) to ASSE 1003 or CSA B356, with a strainer, has to bring it back to 80 or less. The 2021 International Residential Code says the same in §P2903.3.2, and the 2024 IPC text (read in New York State's 2025 adoption) carries §604.8 unchanged.

The floors are in Table 604.3, and they are flowing pressures at the fixture outlet under peak demand, not the number on a gauge at rest. Most fixtures need 8 psi flowing; anything with a pressure-balancing or thermostatic mixing valve, and every tank toilet, needs 20 psi. Where the supply cannot deliver those, §604.7 requires a booster.

You need a test gauge with a female hose-thread coupling and, ideally, a second "max" needle that the working needle pushes up and leaves behind. Without that second needle the test only tells you about the minute you stood there.

1. 1

   Pick the right outlet

   Use a hose-thread outlet on the house side of the pressure-reducing valve: a laundry tub faucet with a hose adapter, or the drain valve on the water heater. An outside bib is the easy choice, but IPC 2021 §604.8 lets the line to a sillcock stay unregulated, so on many houses the outside bib reads street pressure, not what the fixtures see. If you test outside, find out which side of the valve it tees off.

2. 2

   Stop every draw in the house

   Taps off, no toilet refilling, washing machine and dishwasher idle, irrigation off, softener not regenerating, ice maker not filling. One running fixture turns a static reading into a flowing one and you will chase a fault that is not there.

3. 3

   Thread the gauge on and open the outlet fully

   Hand-tight with the washer seated. Open the valve all the way; the needle settles in a second or two. That is your static pressure. Write it down with the time.

4. 4

   Open a fixture somewhere else

   Run a tub spout or a second outdoor tap wide open and read the gauge again. That is flowing (dynamic) pressure at the test point. A small drop is friction doing its job; a collapse points at a restriction between the meter and the gauge.

5. 5

   Reset the max needle and leave it overnight

   Close the fixture, let the gauge settle back to static, then turn the max needle down against the working needle. Leave the gauge on through a night, so the water heater cycles at least once with nothing drawing.

6. 6

   Read three numbers in the morning

   Static now, the max needle, and the flowing reading from step 4. Those three together tell you which problem you have. One number on its own rarely does.

Static is the pressure with nothing flowing. It is the number §604.8 governs and the one a PRV is set to. Flowing is what is left at the gauge while water moves; the difference is friction and restriction upstream of the test point. The fixture floors in Table 604.3 are flowing numbers, so a house can read a healthy static and still starve a shower upstairs.

The third number is the one that breaks things. Once a PRV, a check valve or a backflow preventer sits on the service, the house is a closed system. When the water heater fires with no tap open, the heated water expands and has nowhere to go, so pressure climbs until a tap opens or the relief valve weeps. IPC 2021 §607.3 requires a thermal expansion control device on the heater's cold supply, downstream of all of those valves, sized so the system stays within the §604.8 limit; the IRC carries it in §P2903.4.1 and §P2903.4.2.

Read the three numbers together. The pattern matters more than any one figure.

High pressure is the case worth acting on fast: it is in every supply line, every valve seat and every flex connector all day. A valve set too high or failed open is covered in the pressure-reducing valve guide. Before and after any fix, run the meter test EPA WaterSense describes: read the meter, use no water for two hours, read it again. Any movement is a leak, and the leak cost calculator puts a number on it.

Low flowing pressure with a good static is a restriction, and in an older house the usual one is galvanised pipe scaled down to a fraction of its bore. No valve setting fixes that; the answer is new pipe, and copper, CPVC or PEX is the next decision. A single weak shower on an otherwise healthy system is usually the valve itself, and shower valve replacement covers the cartridge and the body.

Static pressure from height is one division: 1 psi of pressure holds up 2.31 ft of water. A tank or tower whose water surface sits 115 ft above your tap gives 115 ÷ 2.31 = 49.8 psi static. The same rule costs you on the way up: a shower 20 ft above the gauge starts 20 ÷ 2.31 = 8.7 psi lower before any water moves.

Flowing pressure needs friction as well, which depends on flow, pipe size and length. That is what the water pressure calculator works out, run by run, so it is not repeated here.

On a well there is no street pressure. The pump runs until a pressure switch reaches its cut-out, stops, and restarts when the pressure falls to its cut-in, so a gauge on a well system swings between those two settings by design. Read the pair on the switch or the pump install record, then check the tank: with the pump off and the tank drained, its air pre-charge should sit 2 psi below the cut-in, per Amtrol's guidance. A pump that short-cycles on every tap usually points at a tank that has lost that charge. The pump type matters too; see jet vs submersible.