Low Water Pressure in Washington, DC Area Homes

Start with a simple map of the problem

Before you change anything, spend five minutes running water around the house. Write down what you find, because the pattern points to the cause far better than a guess does.

1. Open the kitchen faucet on cold, then on hot.
2. Try a bathroom sink and a shower on an upper floor.
3. Try a basement laundry tap or utility sink, if you have one.
4. Open an outdoor hose bib, in a season when it is not shut down for winter.
5. Ask a neighbor on the same block whether their flow has changed.

Why is only one faucet or shower slow?

A single weak outlet is a fixture problem in almost every case. Unscrew the aerator from the tip of the spout, or take off the showerhead, and look for grit and white scale. DC Water describes its water as moderately hard and varying by location and season, and hard water leaves mineral scale in screens and showerheads over time. Soak the parts in white vinegar, scrub them with an old toothbrush, and put them back. DC Water gives this same advice for cleaning aerators, and adds that worn or damaged aerators should simply be replaced.

If flow is still poor with the aerator removed, the restriction is inside the faucet or shower valve. Cartridges clog and wear out, and older two-handle valves can shed bits of washer into the line. That is a job for someone who does faucet repair and replacement, or, for a tub and shower, shower valve work.

What if only the hot water is weak?

When cold water runs strong and hot water dribbles at every tap, the issue sits between the water heater and the fixtures. Common culprits are a partly closed valve at the heater, a clogged heat trap or dip tube, or sediment that has built up in an older tank. Tankless units have inlet screens that collect debris and can lose flow when they need descaling. A plumber can check the heater connections and tell you whether a flush and repair will do or whether the unit is near the end of its life. Our guide to repairing or replacing a water heater walks through that decision, and you can also reach water heater repair help in the District.

Whole-house low pressure: check the valves first

If every fixture is weak, look at the main shutoff before anything else. In many rowhouses and older homes it is in the basement near the front wall, where the service pipe comes in from the street. A valve that was closed for a repair and only partly reopened is a common and easily fixed cause. Turn it fully open, counterclockwise, but do not force a stiff old gate valve; if it will not move or starts to drip at the stem, leave it for a plumber.

The pressure reducing valve

Many homes have a pressure reducing valve, often a bell-shaped brass fitting just after the main shutoff. Its job is to bring high street pressure down to a safe level for the house. DC Water notes that high pressure is normally defined as more than 80 psi inside a building, and that the District of Columbia Plumbing Code requires a pressure reducing valve when pressure goes above that. The Department of Energy's Building America guidance likewise says most plumbing codes require one on domestic systems where supply pressure exceeds 80 psi.

These valves wear out. When one fails it can drift low and starve the house, or fail open and let full street pressure through. An inexpensive screw-on gauge at a hose bib or laundry tap will show you a number to give the plumber. If the reading is low and the street side is normal, the valve may need adjusting or replacing. If the reading is high, that matters too: DC Water lists noisy pipes, water hammer, dripping faucets and leaks as effects of high pressure, which is why a failed-open valve should not be ignored.

Pressure varies by neighborhood because of elevation and how each utility divides its system into pressure zones. DC Water has run a program in one part of Ward 8 that raised pressure and installed pressure reducing valves in affected homes at no cost to the owner. If your utility has done work that changed pressure on your street, it usually notifies the homes involved.

Could old galvanized pipe be the reason?

Half of the District's homes were built before the late 1950s, and older rowhouses there, like older homes in inner suburbs such as Takoma Park and Hyattsville, may still have some galvanized steel water pipe. Over decades, the inside of galvanized pipe corrodes and narrows, so flow falls off slowly, year after year, and is usually worst on upper floors. There is a second reason to look closely: DC Water warns that galvanized household pipes can collect lead released from past lead service lines, and it recommends fully replacing galvanized plumbing along with any lead service line.

DC Water's Lead Free DC program has several replacement options for service lines, and its Service Line Inventory Map shows the pipe material on record for a property. Inside the house, replacing old galvanized lines is a whole-house repiping project, which also tends to restore strong, even pressure.

Is there a leak stealing your pressure?

A sudden drop, rather than a slow decline, often means water is going somewhere it should not. Turn off every tap and appliance and watch the water meter. If the dial or low-flow indicator keeps moving, you have a leak. Look for damp spots in the basement, wet soil or unusually green grass over the service line, or a hissing sound in a wall. A plumber who does leak detection in DC can locate a hidden leak without opening up walls at random. If the leak is on the line between the meter or property line and the house, that is a water service line repair. In cold snaps, a frozen section of pipe can also cut flow to part of the house; see our tips on keeping DC-area pipes from freezing.

Who is responsible: the utility or you?

The split between public and private pipe depends on the utility, so check yours before you call.

• Washington, DC: DC Water replaces service pipe in public space; the pipe on private property is the owner's responsibility. Customer service is 202-354-3600, and the DC Water emergency command center is 202-612-3400.
• Arlington County: the County owns the line from the main to the meter, including the meter box, and the owner has the line from the meter into the house. The County's emergency hotline is 703-228-6555.
• Montgomery and Prince George's counties: WSSC Water serves most homes, with part of each service line owned by the utility and the rest by the customer. Its emergency line is 301-206-4002.
• Fairfax County: Fairfax Water takes calls, including after-hours emergencies, at 703-698-5800.
• Leesburg: the Town maintains lines up to and including the meter, and the owner has the line from the meter box to the house.
• Prince William County: Prince William Water runs an emergency dispatch line at 703-335-7990.

If your area is not listed, the number is on your water bill. Our list of towns we cover also links to local pages with utility details.

When to call a plumber

Clean the aerators yourself. Call a plumber when the problem is inside a valve, when the pressure reducing valve needs adjusting or replacing, when the gauge reads above 80 psi, when the meter shows a leak, or when you suspect old galvanized pipe. If you are unsure where the trouble is, a plumbing inspection covers the main valve, the pressure reducing valve, the water heater connections and the visible piping in one visit.