Low water pressure can bring to mind clogs from tree roots invading pipes outside and hidden leaks that bring nothing but trouble. But if low water pressure is at one faucet only, chances are the fix is just a matter of unscrewing the end piece on the faucet, called the aerator. The aerator can become clogged with sediment, resulting in low water flow or even spitting or crooked water flow. In areas with hard water, aerators can clog up very quickly, but even soft-water areas aren't immune to the problem.
It's possible that the low water pressure you see is caused by something a little further down the line, but the aerator is so simple to check — and almost always the cause of the problem — that you should start there.
What's Going on Inside the Aerator?
The faucet aerator has three main parts. There's the housing or case, which is what you see when you look at the faucet. There's the aerator insert, and then there's a rubber washer. Scale can build up on the top of the insert, making it harder for water to flow through. You may also see small pebbles that are just loose sediment.
When you unscrew the aerator (use a special wrench for aerators set inside the faucet; you can get these at home improvement stores), have a cup of plain white vinegar by the sink. Once the aerator's out, brush away loose sediment and dunk everything into the vinegar. Let it sit for at least 15 minutes, and then scrub everything with an old but clean toothbrush. Try to brush out the scale from the insert. Some inserts come apart into smaller pieces; if yours does, that will let you clean it more thoroughly.
Before you replace the aerator, turn on the water. The stream will appear rough as it's not being aerated. If the stream is not very strong, then you know you have another problem to deal with (more on that in a little bit). If the stream is strong, replace the aerator (obviously turn off the water first and put the aerator back together) and turn the water on again. If the pressure is back to normal, you're done.
Don't Discount the Possibility That the Aerator Is Defective
With the move toward reducing water use in many states, a lot of bathroom sink aerators are now very low-flow, with 1.2 gallons per minute (GPM) and even 0.5 GPM available. You shouldn't have much of a water pressure loss with these. If you do — say, the water coming out of the faucet without the aerator flows well but the cleaned aerator makes the water barely flow — you could have a defective aerator insert.
Problems Literally Down the Line
Other issues that could cause the low flow, if the aerator appears OK, are blockages in the line leading up from the wall to the faucet and blockages just behind the wall in the pipes. These blockages are usually caused by scale buildup but need to be removed manually.
Whether you need a better aerator or need to clear out a water line, a plumber can take care of those easily and safely. You shouldn't have to deal with low water pressure when the problem can be cleared away quickly.
Contact a local plumber to learn more.