Is it one fixture, hot water only, or the whole house?
Low water pressure usually traces to one fixture, the hot side, or the supply into the house, and a few minutes of testing shows which. It's easy to guess wrong, because a weak kitchen faucet is a different problem from weak water everywhere.
Turn on the hot and cold taps at each sink, shower, and tub in the house. Pay attention to three things:
- Is one fixture weak while the rest run normally?
- Is cold water fine but hot water weak everywhere?
- Is everything weak, hot and cold?
Each answer points somewhere different. One weak fixture usually points to that fixture. Weak hot water points to the water heater side. Weak everywhere points to the supply coming into the house.
Write down what you find. It's the first thing a plumber will ask, so it helps to have it ready.
What if only one faucet or shower is weak?
Start with the aerator, the small screen at the tip of most faucets. Minerals and grit collect in it, and the water slows to a dribble.
Hard water can be a reason. The City of Phoenix Water Services 2025 Water Quality Report lists total hardness of 172 to 302 ppm in its distribution system. Other Valley providers report different figures, and some don't publish one, so check yours. Where water is hard, scale can build up on screens and small openings.
To check the aerator, unscrew it by hand, or use pliers wrapped in a cloth to protect the finish. Look for grit or white crust. If you see it, soak the aerator in white vinegar until the deposits loosen, rinse it, and put it back. Some manufacturers warn that vinegar can harm certain finishes, so read your fixture's instructions first.
If the aerator is clean and the flow is still weak, look at the shutoff valve under the sink. A valve that isn't fully open holds back flow. Turn it gently to be sure it's open all the way. If that doesn't help, the problem may be inside the faucet, such as a worn cartridge. That's a job for faucet repair.
A single weak shower often means a scaled showerhead, and the same vinegar approach applies, with the same warning about finishes. If the head is clean, the valve behind the wall is the next suspect, and that's work for a plumber.
What if only the hot water is weak?
When cold water is strong everywhere and hot is weak everywhere, look at the hot side. The usual suspects:
- The water heater. A plumber can check the tank, including for sediment, and flush it if that's the issue.
- The valves on the heater's water lines. A valve that isn't fully open can restrict what gets through.
- A leak on the hot line. Water escaping inside a wall or under a slab doesn't reach the tap.
If only one fixture has weak hot water and its cold side is fine, the trouble is usually at that fixture. Go back to the aerator and valve checks above.
Leave the heater's gas connections and controls to a licensed plumber. If you smell gas at any point, leave the house and call your gas utility or 911.
What if the whole house is weak?
Weak water everywhere means the problem sits before the line splits into hot and cold. Check these in order:
- The main shutoff valve. It's where the water line enters the house. If it was left partly closed after some work, flow drops. Make sure it's fully open.
- The pressure regulator. Some homes have one. It keeps incoming pressure steady. If it fails or drifts, pressure can drop or climb too high. A plumber tests it with a gauge and adjusts or replaces it. This isn't one to adjust by feel.
- Your water provider's side. Ask a neighbor if their pressure is weak too. A repair or a problem on the provider's system can affect a whole street. Call your own water provider to ask. Which part of the line is theirs and which is yours varies by provider, so confirm it with yours.
- A leak between the meter and the house. A leak in the line that feeds your home can pull pressure down. Clues are a soggy spot in the yard, the sound of water running when everything is off, or a bill that jumped. That points to water line repair.
- Debris in a valve or screen. Grit can block a strainer or valve. A plumber can check.
Pressure that's too high is a problem too. It strains pipes, fixtures, and appliances, so a whole-house gauge reading is worth having whichever way the problem runs.
When should you call a licensed plumber?
Call if the whole house is weak and your water provider says its side is fine, if hot water is weak on an older heater, if you suspect a leak, or if the easy checks above didn't fix a single fixture.
A licensed plumber can put a gauge on the line, test the regulator, look at the heater side, and find a hidden leak if there is one. That beats buying parts and hoping.
If you see water pooling outside, or hear it running when nothing is on, close the main shutoff and call a licensed plumber right away. If water is anywhere near electrical, keep clear of it, close the main only if you can reach it safely, and call right away.
Brian's spent 20+ years as a plumber in the Valley. If your own checks don't explain it, book a water pressure diagnosis and get a clear answer.
Common Questions
If cold water runs normally and only the hot side is weak, the trouble is on the hot side: the water heater, its valves, or the pipes leaving it. A plumber can check.
Yes. A leak in a supply line can lower the pressure at your fixtures. Clues include a wet spot, the sound of running water when nothing is on, or a water bill that jumped for no reason.
A regulator is a valve that keeps incoming water pressure steady for the house. Some homes have one, and a plumber can confirm whether yours does.
Yes. Pressure that is too high strains pipes, fixtures, and appliances. A plumber can test it with a gauge and adjust or replace a regulator.
Ask a neighbor and call your own water provider. Where the provider's responsibility ends and yours begins varies by provider, so confirm it with yours.
