Low water pressure is easy to dismiss — until it isn't. A weak shower stream might seem like a minor annoyance, but it can be a symptom of something serious happening inside your pipes, your supply system, or your pressure regulation. Here are the 6 most common causes, how to diagnose them, and what each one costs to fix.

Cause 1: Partially Closed Shutoff Valve

The most common and most easily fixed cause of sudden low pressure — and the first thing to check. There are two main shutoffs: the main house shutoff (near where the water line enters) and the meter shutoff (near the street). If either was recently serviced or partially closed, pressure drops significantly. Check both and confirm they're fully open. A ball valve should have the handle parallel to the pipe. A gate valve should be turned fully counterclockwise.

Cause 2: Failing Pressure Regulator

Most homes have a pressure regulator (PRV) installed where the main water line enters. It's typically a bell-shaped device near the main shutoff. When it fails, it usually drops pressure too low — or less commonly, lets it run too high. A failed PRV causes sudden, whole-house pressure changes. Replacement costs 00–00 and is a job for a licensed plumber.

Signs the PRV is failing: sudden unexplained pressure change, pressure that varies throughout the day, gauge reads below 40 PSI with valves fully open, PRV is 10–15 years old.

Cause 3: Pipe Corrosion or Buildup

Homes with galvanized steel pipes experience significant internal corrosion over decades. The inside of the pipe literally shrinks as rust and mineral deposits build up, restricting water flow. This shows up as gradually decreasing pressure over months or years, often in specific areas first. The fix — repiping — is expensive, but the cost is nearly always less than dealing with a catastrophic pipe failure later.

Cause 4: Clogged Aerators or Showerheads

If low pressure is limited to one fixture, the problem is almost certainly a clogged aerator or showerhead — not a whole-house issue. Mineral deposits accumulate in the small screens and perforations over time. This is a simple DIY fix:

• Unscrew the aerator from the faucet tip — usually by hand or with pliers
• Soak in white vinegar for 30 minutes to dissolve mineral deposits
• Rinse and reinstall — pressure should return immediately
• For showerheads, fill a bag with vinegar, secure around the head with a rubber band, let soak for an hour

Cause 5: Hidden Water Leak

A significant hidden leak diverts water before it reaches the fixture, dropping pressure throughout the affected area. Signs a hidden leak is causing your pressure problem:

• Pressure drops even when no one else is running water
• Water bill has increased without explanation
• You hear running water when all fixtures are off
• Wet spots, staining, or soft spots on ceilings, walls, or floors
• Your water meter continues to spin when all water in the house is off

If you suspect a hidden leak, call a plumber immediately. Modern leak detection uses acoustic equipment and thermal imaging to find leaks without unnecessary wall damage.

Cause 6: Municipal Supply Issues

Sometimes the problem isn't your home — it's the water main. Peak demand hours, nearby construction, or aging municipal infrastructure can reduce pressure at the meter. To confirm: ask neighbors if they're experiencing the same drop, check your utility's outage page, or test pressure at the meter connection point. If municipal pressure consistently runs below 40 PSI, a booster pump (00–00 installed) can compensate.

How to Diagnose Your Low Pressure Problem