Why Is Water Pressure Low at Just One Faucet or Shower?

What it usually looks like

• One faucet or shower runs weak while every other fixture has normal pressure
• The problem is only on the hot side, or only on the cold side, of that fixture
• Flow got worse right after plumbing work, a water heater replacement, or a utility main flush
• The shower head sprays unevenly or some nozzles are blocked
• The faucet sputters or spits air before settling into a weak stream
• A single-handle faucet is hard to turn or feels gritty

Likely causes, most common first

1. A clogged aerator or shower head

   The screen at the tip of a faucet, or the tiny nozzles in a shower head, catch sediment, pipe scale and bits of solder or plastic. Any time the water is shut off and turned back on, the pipes shed debris downstream, and it collects at the first screen it hits. This is the first thing to check and the easiest to fix.

2. A worn or scaled faucet cartridge

   Single-handle faucets and most shower valves use a cartridge with small ports that mix hot and cold. Mineral scale, a torn seal or a swollen cartridge narrows those ports. When only the hot side is weak at a shower, scale in the cartridge is the likely culprit because hot water deposits minerals faster.

3. An angle stop not fully open or failing

   The small shutoff valves under a sink or behind a toilet are often multi-turn valves with a rubber washer. They get bumped partly closed, or the washer swells and droops into the flow. Compression stops from the 1980s and 90s are especially prone to this.

4. A kinked or collapsed supply line

   Braided flex connectors can kink behind a vanity, and the rubber liner in old ones can delaminate and flap closed under flow. A supply line that looks fine from the outside can be nearly shut inside.

5. A pressure-balancing spool stuck in a shower valve

   Most shower valves have a spool that shifts to keep temperature steady when a toilet flushes. If it sticks to one side, it chokes one supply. You get a weak shower that may also run cold or hot unexpectedly.

6. A corroded branch line to that fixture

   In a house that still has galvanized steel branches, the run to one distant bathroom can be rusted nearly shut while the rest of the house, already repiped or on shorter runs, flows fine. This is common in older homes that were partially updated.

Safe things to check yourself first

• Unscrew the aerator or shower head, rinse out the screen, and soak it in white vinegar for an hour if it is crusted
• Under the sink, turn each angle stop fully counterclockwise and confirm it moves freely
• Look at the flex supply lines for kinks or bulges and make sure they are not pinched by drawers or cabinets
• Remove the shower head entirely and run the arm; strong flow there means the head is the problem
• Test hot and cold separately to narrow it to one side

How we diagnose and fix it

• Test flow at the supply stops with the fixture disconnected to confirm whether the restriction is in the fixture or behind the wall
• Replace the cartridge, pressure-balancing spool or aerator and clean debris from the valve body
• Swap failed multi-turn angle stops for quarter-turn ball-type stops and replace suspect supply lines
• Open the wall or crawlspace only when the branch line itself is the problem, and replace that run with PEX or copper
• Show you what came out of the fixture so you know whether to expect it again, and recommend a sediment filter when the house has a sand or scale source

Questions people ask