Is Low Water Pressure a Plumbing Emergency?
Not always — but it depends on the cause. Suddenly low pressure throughout your entire house can indicate a serious leak, a main line break, or a water main issue. Gradually worsening pressure over months or years is usually a sign of pipe corrosion or mineral buildup. Either way, low pressure that can't be explained by a city water supply issue should be investigated by a licensed plumber.
Cause 1: Failing Pressure Regulator Valve (PRV)
Most homes in LA have a pressure regulator valve (PRV) where the water main enters the house. This valve reduces incoming city water pressure (typically 80–150 PSI) to a safe household level (40–60 PSI). When the PRV fails, pressure can drop dramatically — or spike dangerously high. A failed PRV is one of the most common causes of sudden whole-house low pressure in LA. Replacement typically costs $300–$600.
Cause 2: Corroded or Clogged Pipes
Homes built before 1985 in Los Angeles very commonly have galvanized steel water supply pipes. These pipes corrode from the inside out, building up rust and mineral scale that progressively chokes water flow — like plaque in an artery. Low pressure in a home with galvanized pipes is a strong signal that repiping is needed. This problem cannot be fixed by clearing a clog — the entire pipe run needs replacement.
Cause 3: Undetected Water Leak
A significant water leak in your supply line — inside a wall, under a slab, or in the yard — will cause an unexplained drop in water pressure. Often these leaks are invisible but can be detected by your water meter (if it spins while all fixtures are off, you have a leak). Leak detection service uses electronic listening equipment and thermal imaging to pinpoint leaks without destructive probing.
Cause 4: Partially Closed Shutoff Valve
If your home's main shutoff valve or a secondary shutoff was partially closed after service work, this can cause house-wide low pressure. Check the main shutoff (usually near the water meter) and ensure it is fully open. Also check shutoffs under sinks and near appliances — a partially closed valve causes localized pressure loss.
Cause 5: Hard Water Mineral Buildup at Fixtures
Los Angeles has some of the hardest water in the US, with significant calcium and magnesium content. Over time, mineral deposits build up inside faucet aerators, showerheads, and fixture valves — restricting flow. If pressure is low only at specific fixtures, try removing and soaking the aerator in white vinegar overnight. If this resolves it, the pipe is fine and the issue is fixture-specific buildup.