Why Is My Water Pressure Low?
Low pressure in a Phoenix home usually points to one of four things. Hard-water buildup in supply lines, a failing pressure-reducing valve (PRV), a partially closed shut-off, or a hidden leak. The first three you can diagnose yourself; the fourth needs a tech.
Pick up an inexpensive hose-bib pressure gauge and read static pressure at the outdoor spigot closest to your meter, with everything off. Phoenix delivers 40 to 80 PSI. Under 40 means the PRV closed up; over 80 means it gave out. Either way, replace the PRV.
If the gauge reads outside that range, or pressure feels weak with normal gauge readings, call 602-560-8989. We will troubleshoot it with you on the phone before we send anyone out.
Common Causes
Mineral Buildup in Pipes
Phoenix-area water at 12 to 20 grains per gallon leaves calcium and magnesium deposits inside supply lines. Pre-1970 galvanized steel mains in older central Phoenix neighborhoods like Encanto and Coronado can narrow from 3/4 inch inside diameter to under 1/4 inch. You feel it first in the master shower, and if hot is weak but cold runs fine, the buildup is on the hot side only.
Partially Closed Shut-Off Valve
The main shut-off at the meter or where the line enters the house is the first place to check, especially after recent plumbing work. Half-closed gate valves are one of the most common things we find on a low-pressure call. Plastic-handle angle stops common in 1980s and 1990s Valley homes can stick partially closed once hard water builds up around the stem.
Pressure Regulator Failure
Most Phoenix homes built after 1990 have a pressure regulator (PRV) near the main shut-off, usually a Watts LF25AUB-Z3 or Wilkins NR3. PRVs last 10 to 15 years; hard water often shortens that to 8. A failed PRV either strangles pressure under 40 PSI or spikes it past 100 and pops the water heater T&P valve.
Hidden Leak (Often Slab)
A leak in the main service line or under the slab diverts water before it reaches your fixtures, dropping pressure house-wide. Watch for unexplained water-bill bumps, warm spots on tile floors, or the meter dial spinning with every fixture off. Any of those means leak detection, not aerator cleaning.
Municipal Supply Issues
Phoenix Water Services and surrounding city utilities occasionally cut pressure for main repairs or during peak summer demand. If the whole neighborhood is weak, ask a neighbor before calling a plumber. Phoenix delivers 40 to 80 PSI at the meter; anything reliably below 40 with no internal cause is a city-side issue.
Corroded or Undersized Pipes
Older Phoenix homes often have 1/2-inch galvanized supply lines feeding fixtures that today's code wants on 3/4-inch trunks. Add 50 years of internal corrosion and you can't run two showers at once. If you're opening walls for a remodel, repipe to PEX-A while they're open.
Single-Fixture Pressure Loss
If pressure is normal everywhere except one fixture, the restriction is at that fixture, not the house. Unscrew the faucet aerator or showerhead and soak it in white vinegar overnight. A Moen, Delta, or Kohler cartridge older than eight years that runs slow on both hot and cold has scaled internally and needs replacement.
What Should You Do?
Try This First
- Pick up an inexpensive hose-bib pressure gauge at any hardware store. Screw it onto the outdoor hose bib closest to your meter and read static pressure with no fixtures running. Phoenix Water Services delivers 40 to 80 PSI.
- If static pressure reads 40 to 80 PSI but pressure feels weak inside, the restriction is downstream of the PRV. If it reads under 40, the PRV is failing closed or your main shut-off is not fully open.
- Find the main shut-off (usually in the garage wall or near the water heater) and confirm it is fully open. Quarter-turn ball valves should be parallel to the pipe. Round-handle gate valves turn counterclockwise until they stop, then back off a quarter turn.
- Unscrew every faucet aerator and soak in white vinegar overnight, then rinse. Do the same with showerheads (unscrew, or tie a vinegar bag around the head with a rubber band). Re-test pressure at each fixture after.
- Close every angle stop under sinks and behind toilets all the way, then reopen fully. Stuck-partially-closed valves are common in Phoenix homes once hard water sits in the stem.
- If only one fixture is weak (just a shower or just one faucet, not the whole house), the restriction is local. Replace that fixture's cartridge or aerator before opening walls. For a slow showerhead, also check the in-line flow-restrictor disc behind the head.
- Read your water meter with all fixtures off and every appliance idle, wait 30 minutes, and read again. Any movement at all means a hidden leak, and that is a leak detection call.
Call a Pro If...
- Hose-bib gauge reads under 40 PSI with the main shut-off confirmed fully open (PRV is failing and needs replacement)
- Pressure stays weak throughout the house after aerators are clean and valves are confirmed open (restriction is internal piping)
- Your home has pre-1970 galvanized steel mains and pressure has been declining for years (a repipe-to-PEX evaluation is overdue)
- Water bill jumped 20% or more with no usage change (hidden leak before your fixtures, often a slab leak)
- You hear running water with everything off, or notice warm spots on tile floors (that is a slab leak signature)
- Hose-bib gauge reads over 80 PSI and the water heater T&P valve drips (PRV failed open, replace it before joints fail)
- Pressure is intermittent and the PRV is more than 10 years old (PRV cycling, replace before it fails outright)