Low water pressure is one of the most common complaints we hear from Northern Virginia homeowners — especially in summer, when irrigation systems, pool fills, and increased household demand all hit at once. The good news: most causes of low water pressure are fixable, and some you can handle yourself. Here's how to figure out what's going on.
First: Is It Your Whole House or Just One Fixture?
This is the most important question. Turn on faucets in different parts of your home — kitchen, bathrooms, hose bib outside. If pressure is low everywhere, the problem is upstream: the main supply line, pressure regulator, or the municipal supply itself. If it's only one fixture or one area of the house, the problem is local to that fixture or the pipes serving it.
This distinction saves a lot of diagnostic time, so figure it out before calling anyone.
The 7 Most Common Causes
Failing Pressure Regulator
Most homes in Northern Virginia have a pressure reducing valve (PRV) — usually a bell-shaped brass fitting near where the main water line enters the house. It's set to keep your household pressure between 45–80 PSI. When a PRV fails, it can cause pressure to drop sharply (or occasionally spike). PRVs typically last 10–15 years. If yours is older and you're seeing whole-house low pressure, this is the first thing to check. A plumber can test the PRV output with a simple gauge and replace it in a few hours if needed.
Partially Closed Main Shutoff Valve
This sounds obvious, but we see it all the time — especially after any recent plumbing work. Your main shutoff valve (usually near the water meter or where the main enters the house) may have been turned off and not fully reopened. A gate valve needs to be turned all the way counterclockwise to be fully open. A ball valve handle should be parallel to the pipe. Check this first — it's a 30-second fix.
Clogged Aerators and Showerheads
If pressure is low only at specific faucets, the culprit is almost always a clogged aerator — the small mesh screen at the tip of the faucet. In Northern Virginia, our water is moderately hard, which means mineral deposits build up over time and restrict flow. Unscrew the aerator, soak it in white vinegar for an hour, and rinse it out. Same for showerheads — remove it and soak it overnight in vinegar. This fixes the problem about half the time for single-fixture low pressure.
Mineral Buildup Inside Pipes
In homes with galvanized steel pipes (common in Fairfax and Loudoun County homes built before 1980), mineral deposits and rust build up on the inside of the pipe walls over decades, gradually narrowing the passage water flows through. This is a slow, progressive problem — pressure gets a little worse each year. If your home is older and you've never had the pipes inspected, a camera inspection can show you exactly how much buildup you're dealing with. Repiping is the long-term solution; it's a bigger project, but it solves the problem permanently.
A Leak in the Supply Line
A leak anywhere in your supply line bleeds off pressure before water reaches your fixtures. Signs include unexplained wet spots in the yard, a water meter that's running when everything is off, or a water bill that's suddenly higher than usual. Check your meter: shut off all water in the house and watch the meter for 15 minutes. If it's still moving, you have a leak. This needs a plumber — underground supply line leaks are not a DIY repair.
Municipal Supply Issues
Sometimes the problem isn't your house at all — it's the water authority. Summer demand in Loudoun and Fairfax counties peaks in June and July as irrigation systems run constantly. Call Loudoun Water or Fairfax Water and ask if they're aware of any pressure issues in your area. If neighbors are reporting the same thing, the problem will resolve on its own. If you're the only one affected, the problem is on your side of the meter.
Water Heater Issues (Hot Water Only)
If your pressure is fine with cold water but low with hot, the problem is isolated to your water heater. Sediment buildup in the tank, a partially closed shutoff valve on the water heater, or a failing pressure relief valve can all restrict hot water flow. Flushing the tank annually prevents sediment buildup. If you haven't flushed yours in several years — or ever — this is a likely culprit for hot-side pressure issues.
When to Call a Plumber
Try the simple fixes first — check the main shutoff, clean aerators, test the pressure. If you've done all that and pressure is still low throughout the house, it's time to call us. The most common root causes we find in Northern Virginia homes are failing PRVs (especially in homes built in the 80s and 90s), galvanized pipe buildup in pre-1980 homes, and undetected supply line leaks.
A diagnostic visit takes less than an hour and gives you a clear answer. We won't recommend a $5,000 repipe when a $300 PRV replacement will solve the problem.
Side-by-Side Diagnosis Guide
| Symptom | Most Likely Cause | DIY or Plumber? |
|---|---|---|
| Low pressure everywhere, sudden | PRV failure or closed shutoff | Check shutoff yourself; PRV needs plumber |
| Low pressure everywhere, gradual | Pipe buildup or supply issue | Plumber for inspection |
| One faucet only | Clogged aerator | DIY — clean or replace aerator |
| One showerhead only | Mineral buildup in head | DIY — vinegar soak overnight |
| Hot water only low | Water heater sediment or valve | Flush tank yourself; valve needs plumber |
| Meter running with water off | Supply line leak | Plumber immediately |
Still Can't Figure Out the Cause?
We diagnose low water pressure problems across Northern Virginia every week. One visit, clear answer, honest recommendation.
Call (703) 939-4473