Q: The water pressure in our single-family home was never great, but this winter, it became awful. The pressure gauge at the main water inflow to the house is within the normal range. The problem is worst in the primary bedroom’s bath, which is immediately above the water inflow but on the opposite side of the house from the water heater. Our regular plumber was of little help. Any ideas about the cause or solutions?

A: Sometimes there are simple ways to get more water flowing. Other times, the only solution is to replace the pipes — a huge, expensive hassle.

Troy Ray, a plumber at Mallick Plumbing & Heating in Gaithersburg, Md. (301-804-6759; mallickplumbing.com), said he begins by asking people whether the low water pressure affects the whole house. If so, he starts where the water enters the house and checks the pressure just after the pressure-reducing valve, which lowers water pressure coming in from the street to a pressure that’s suitable for indoor use.

Like many water agencies, Fairfax Water, which serves Reston, requires a reducing valve wherever the main water line is pressurized above 80 pounds per square inch. If pressure after the reducing valve is low, which generally means below 40 psi, Ray installs a new valve, and that often solves the problem. But it sounds as if you’ve already ruled that out as your issue.

If low water pressure affects just one room, the first question is whether water is slow to just one or two fixtures or to the whole room. If the sink and shower are limping but the toilet flushes properly and the bathtub spout delivers water at a reasonable rate, the faucet aerator and shower head are almost certainly plugged by mineral deposits or debris from the pipes. “Maybe water got shut off, then turned back on,” said Dan Cochran, plumbing manager at Dwyer Plumbing, Heating & Air in Lorton, Va. (703-922-8220; dwyerplumbing.com).

That would vary the pressure, causing deposits within the pipes to come loose and plug the small openings in the aerator or shower head. Fixing this is fairly easy and not something most homeowners need to pay a plumber to do. You just need to clean or replace the plugged part. Aerators and shower heads screw on. To remove them, unscrew them. (You may need to use pliers, especially for a shower head.) To keep from scratching the finish, wrap a cloth around the metal first.

Sometimes, it’s enough to brush the openings with an old toothbrush and rinse. If an aerator is still plugged, use a pin or needle to poke out grit, or buy a new aerator for a few dollars. (Take the old part with you to the store to find the right size.)

Shower heads can also be replaced, but you might not find one in the same style, so it’s worth trying to clean the one you have. The holes often get plugged by mineral deposits from evaporating water. To remove them, soak the shower head in vinegar for a couple of hours. Or, if you want to clean a shower head without removing it, try partially filling a plastic bag with vinegar, slipping it over the shower head, and securing it with twist-ties, a rubber band or string. After two hours, rinse off the vinegar. For a shower head treated in place, remove the bag and turn on the shower.

If you’re lucky, the vinegar will have softened the deposits enough, so the water pressure pushes the remaining deposits out of the holes. Scrubbing with a toothbrush can help dislodge remaining deposits.

If the low pressure affects the whole room, or in a whole-house situation where the pressure-reducing valve is working, finding and fixing the problem takes more sleuthing. Ray checks for a shut-off valve that is partially closed or asks whether there has been any recent remodeling, in case undersized piping could be a factor.

He also looks at visible plumbing in basements or crawl spaces. One time, in a house with an in-line filter, the filter setting had become stuck midway between the bypass setting and “on.” “I took out the filter, and right away the water pressure was where it should be,” Ray said.

This is where having an experienced plumber is invaluable. If the first plumber you called wasn’t helpful, call a different company. Search for family-owned plumbing companies and ask for a more seasoned plumber. You probably won’t get as much help from a plumber who works for a franchise company focused on specific tasks, such as unclogging drain pipes or installing appliances or water heaters.

Unfortunately, if an experienced plumber can’t find a fixable problem, there is a good chance your home’s low pressure is caused by buildup of rust and grime within the pipes, especially if they are made of galvanized steel. “They become like a closed artery, plugged with rust,” Ray said.

In that case, replacing the pipes is probably the only option, even though it means tearing into walls and maybe ceilings. Get a couple of estimates from plumbers and from any professionals you might need to hire to patch drywall and repaint. Discuss with each of them ways to minimize the collateral damage.

In some parts of the country where drinking water is high in minerals, people sometimes try to treat deposits within water supply pipes — not just drain pipes — with vinegar. Do a Web search for “descale pipes with vinegar” to read up on the basic process.

Landmark Home Warranty, which writes policies that cover specific elements of a home, suggests turning off water to the water heater, opening hot-water taps to drain the pipes, draining two gallons of water from the bottom of the water heater and pouring two gallons of white vinegar into the tank. (How to do this, it doesn’t really explain.) Then you’d turn water to the tank back on and run the taps until you smell vinegar. At that point, close the taps and wait until morning, then run the water until the vinegar smell is gone.

This may work in areas where deposits form quickly — Landmark mentions Arizona, Utah, Texas, Nevada and Idaho — but Ray said it’s not something he has heard of being tried in the Washington area, because the water isn’t as high in minerals. “We still get calcium buildup, but it tends to be at the bottom of a water heater over 20 years if you don’t flush it.” But old galvanized pipes do become clogged with rust. And for that, Ray said, the only option is getting new pipes.

Have a problem in your home? Send questions to localliving@washpost.com. Put “How To” in the subject line, tell us where you live and try to include a photo.