Why is my water pressure low throughout the whole house?

Start with a number. Buy a screw-on water pressure gauge at any hardware store. It threads onto a standard hose-bib spigot, the kind used for garden hoses.

Pick the hose bib closest to where the water line enters the house, often on the front of the home near the meter side. Turn off every water-using fixture and appliance inside. That means faucets, the dishwasher, the washing machine, and the irrigation timer. Any open valve will skew the reading low.

Thread the gauge onto the hose bib hand-tight. Open the spigot all the way. Read the dial.

Normal residential pressure runs 40 to 80 psi. The DOE Building America Solution Center, run with Pacific Northwest National Laboratory, recommends a maximum of 60 psi because higher pressure stresses pipes, valves, and appliances. As that DOE resource guide puts it, "high water pressure can damage plumbing fixtures and appliances and waste water." EPA WaterSense says fixtures operate best between 45 and 60 psi. If your gauge reads in the 40s or 50s and the house still feels weak, the problem is volume, not pressure, often scale or a restricted valve. If it reads below 40, you have a true pressure loss to track down.

Take a second reading with one fixture running. A big drop the moment you open a tap points to a restriction, like a half-closed valve or a clogged filter, rather than a low supply.

Most Phoenix homes on city water have a pressure-reducing valve, also called a PRV. It sits just downstream of the main shutoff, near where the line enters the house. Its job is to knock the street pressure down to a safe household level.

The International Plumbing Code, Section 604.8, requires a PRV wherever the static street pressure is above 80 psi, and it must reduce delivered pressure to 80 psi or less. The code also requires the valve to fail in the open position. That is a safety design, but it means a worn PRV often drifts the wrong way and chokes your flow.

A PRV is a wear part. Internal springs and seats give out, usually after about 7 to 15 years of service in our hard water (a figure that comes from valve manufacturers and the trade, not from code or EPA). When it starts to fail, you see one of a few patterns: pressure that creeps up over hours, pressure that swings around, or pressure that sags everywhere and will not respond when you turn the adjustment screw.

To check it, watch your gauge over time. A reading that slowly climbs well past 80 psi when no water is moving is a classic sign of a PRV that is no longer holding. A reading stuck low that will not budge with adjustment points the same direction. If the valve is the culprit, replacing it restores normal pressure to the entire house at once. For the full symptom list, see our page on the signs a pressure regulator is going bad.

If your PRV checks out, look at the pipes and the valves themselves. These are the quiet causes that build up slowly, so the house feels like it has always been a little weak.

Mineral scale is the big one in Phoenix. The USGS classifies water above 180 mg/L of hardness as very hard, and City of Phoenix water reports total hardness in the range of roughly 170 to 284 mg/L, which works out to about 10 to 17 grains per gallon. That mineral load coats the inside of pipes over the years. In older galvanized steel lines it is worse, because scale and internal rust stack up together and shrink the opening water can flow through. The result is a house where pressure tests fine at the gauge but flow feels thin at every tap.

Partly closed valves are the easiest fix and the easiest to overlook. The main shutoff inside the house and the meter valve at the street should both be fully open. A valve left half-turned after a repair, or a meter valve a utility worker did not fully reopen, will throttle the whole house. Find your main shutoff, usually where the line enters near the water heater or in a front utility area, and confirm it is open all the way.

A clogged whole-house filter acts the same way. If you have a sediment or carbon filter on the main line, a cartridge packed with grit and mineral fines will starve every fixture downstream. Filters have a service life. Swap the cartridge on schedule, or check it first if pressure dropped off gradually after the last change was overdue. A quick test: note the pressure, then bypass or remove the filter housing. If flow jumps right back, the cartridge was the choke point.

Order matters when you work the list. Valves are free to check and free to fix, so confirm them first. A whole-house filter is the next cheapest, usually a few dollars for a cartridge. Scale and a failing PRV come last, because they cost real money to address, scale by repiping a section and a PRV by replacing the valve. Working cheap to costly keeps you from paying for a part that was never the problem.

Sometimes the low pressure is not yours at all. The water utility delivers pressure to your meter, and that supply can drop for several reasons outside your walls.

Aging infrastructure fails more than people expect. An AWWA water science study found roughly 260,000 water main breaks each year across the United States and Canada, with about a third of buried mains more than 50 years old. A break or a repair shutdown near you can pull pressure down across a whole neighborhood. Scheduled flushing, hydrant use by the fire department, and pressure-zone work can do the same thing for a few hours.

There is a fast way to tell the side of the meter the problem is on. Ask a neighbor. If their pressure is low too, the cause is on the utility's side and you call the city, not a plumber. If yours is the only weak house on the block, the problem is between the meter and your fixtures, which is where a plumber goes to work.

You can also test at the meter. A gauge reading taken close to the meter that comes back in the normal 40 to 80 psi range means the city is delivering fine and the loss is inside your property. A low reading right at the meter points back to the utility. When the city confirms a main issue, the fix is simply waiting out the repair, and pressure returns on its own.

The single most useful question is whether the weak flow is everywhere or in one spot. The answer sends you to two completely different repairs.

Whole-house low means every fixture is weak at the same time. That points upstream to the shared supply: the PRV, the main or meter valve, scale in the main lines, a clogged whole-house filter, or the city main. Those are the causes this page covers, and the gauge test is your first move.

One weak fixture means a single faucet or shower is slow while the rest of the house runs fine. That is almost always a local restriction at that fixture, most often a clogged aerator packed with mineral scale, which is common with Phoenix water. The fix is cleaning or swapping that one part, not chasing the whole system. We cover that in detail on our page about low water flow from one faucet and clogged aerators.

So before you worry about a major repair, walk the house. Open the kitchen sink, a bathroom faucet, and a shower. If only one is weak, start there and stay local. If all of them sag together, get your gauge, take a reading, and work the list above from the cheapest cause (a half-closed valve) to the costliest (a failing PRV or a repipe). A clear test up front saves you from paying to replace the wrong part.