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Weak showers and taps that take forever to fill a pot are annoying, but they are also information. What causes low water pressure in a house is usually one of a handful of things, and which fixtures are affected tells you most of what you need to know. One slow faucet is a fixture problem. The whole house losing pressure at once is a supply problem. This guide walks through both, in the order our High Point technicians check them.
Key Takeaways
- One fixture weak means an aerator, cartridge or stop valve. The whole house weak means the supply.
- A partially closed main or meter valve is the most common and easiest fix there is.
- A failed pressure reducing valve causes gradual whole house pressure loss.
- Galvanized pipe corrodes inward and chokes flow over decades.
- On well systems, a waterlogged pressure tank or a failing pump is the usual cause.
First Question: One Fixture or the Whole House?
Walk the house and test the hot and cold side at every faucet, the shower, and the outside spigot. Write down which are weak and whether it is hot, cold or both. That three minute test narrows the cause more than anything else you can do.
One fixture weak on both hot and cold points at the faucet or its supply stops. One fixture weak on hot only points at the water heater or the hot supply to that fixture. Everything weak points at the main supply, the pressure reducing valve, or the pipe feeding the house.
Clogged Aerators and Showerheads
This is the cheapest fix and it is worth ruling out first. The aerator screen on a faucet catches mineral scale and pipe debris, and on hard water it can choke a tap within a couple of years. Unscrew it, soak it in vinegar overnight and brush it clean.
Showerheads do the same thing across their spray holes. If scale keeps coming back quickly, the underlying issue is water hardness rather than the fixture. A hard water test tells you where you stand, and our post on the signs of hard water covers the other symptoms that usually show up alongside it.
A Partly Closed Valve
It sounds too simple, but it is one of the most common causes we find. After any plumbing work, a main shutoff or meter valve sometimes gets left short of fully open. A gate valve that looks open can also be partly seized. Both throttle the whole house.
Check the main shutoff where the line enters the house and the valve in the meter box. Open each fully, then back it off a quarter turn. If a valve feels gritty or will not move, it needs replacing with a quarter turn ball valve rather than forcing.
A Failing Pressure Reducing Valve
Most homes on city water have a pressure reducing valve near where the supply enters, because street pressure is usually too high for household plumbing. These valves wear out, typically somewhere between ten and twenty years, and when they fail they usually fail low.
The giveaway is gradual whole house pressure loss with no other explanation, sometimes with pressure that changes through the day. A gauge on an outdoor spigot confirms it. The opposite problem is covered in our post on high water pressure in the house, and the same valve is usually the answer either way.
Corroded or Undersized Pipes
Galvanized steel pipe rusts from the inside. Over decades the internal diameter closes up with scale until a three quarter inch pipe passes what a quarter inch pipe should. Homes built before the 1960s that still have original galvanized supply lines often have this, and it gets worse every year.
You cannot clean that out. The fix is repiping the affected runs, usually in PEX or copper. Our comparison of PEX versus copper covers the choice, and pipe repair and replacement is the service side.
Leaks Between the Meter and the House
A break in the service line loses pressure before the water ever reaches your fixtures. Look for a patch of grass that stays green in dry weather, soggy ground along the line, or a meter that keeps moving when everything inside is off.
This is not a repair to guess at, because the line is buried and may run under a driveway. Our leak detection service locates it before anything is dug up, and our post on underground pipe burst signs covers what to watch for.
If You Are on a Well
Well systems lose pressure for different reasons. A waterlogged pressure tank makes the pump cycle on and off rapidly and gives you pressure that surges and drops while a tap runs. A failing pressure switch holds the system at the wrong cut in point. A worn pump simply cannot make the numbers it used to.
Sediment in the well or a clogged intake screen shows up as pressure that falls off during heavy use and recovers when the system rests. Our post on signs a well needs repair goes through each symptom, and well pump repair and replacement is what fixes it.
| What you notice | Likely cause | Fix |
|---|---|---|
| One faucet weak, hot and cold | Clogged aerator or bad cartridge | Clean or replace the part |
| One fixture weak on hot only | Water heater or hot supply line | Service the heater, check the stop |
| Whole house weak, came on suddenly | Partly closed valve or service line leak | Check valves, then detect |
| Whole house weak, got worse slowly | Failing pressure reducing valve | Replace the PRV |
| Old home, all fixtures weak for years | Corroded galvanized pipe | Repipe the affected runs |
| Pressure surges and drops on a well | Waterlogged pressure tank | Recharge or replace the tank |
What Causes Low Water Pressure: Frequently Asked Questions
What causes low water pressure in a house?
Common causes are clogged aerators, a partly closed main or meter valve, a failing pressure reducing valve, corroded galvanized pipe, and a leak in the service line. On well systems, a waterlogged pressure tank or a worn pump is usually behind it.
Why is only one faucet low on pressure?
The problem is at that fixture. Start with the aerator screen, which collects scale and debris. If cleaning it does not help, the faucet cartridge or the small stop valve under the sink is likely restricted or partly closed.
How do I test my water pressure at home?
Screw a pressure gauge onto an outdoor spigot or the washing machine bib and read it with nothing else running. Between 40 and 60 PSI is normal. Under 40 explains weak fixtures, and over 80 is high enough to damage the system.
Can a water heater cause low hot water pressure?
Yes. Sediment in the tank, a partly closed inlet or outlet valve, or a broken dip tube can all restrict hot water flow while the cold side stays normal. If only the hot side is weak everywhere, start at the heater.
Does low water pressure mean I have a leak?
Not always, but it is one of the possibilities worth ruling out. Read the meter with everything off. If the low flow indicator moves, water is escaping somewhere between the meter and your fixtures, and that needs finding before anything else.
Will replacing old pipes fix low water pressure?
If the cause is corroded galvanized pipe, yes, and it is the only real fix. Scale inside old steel pipe cannot be cleaned out. Repiping in PEX or copper restores full flow. If the pipes are copper or PEX already, look at valves and the PRV first.
Water Pressure Help Across High Point and the Triad
We can test your pressure, trace the cause and tell you what it takes to fix it, with the price up front. All Star Plumbing of the Triad has been family owned in High Point since 2007 and serves Greensboro, Winston-Salem, Kernersville and the towns around them. Call (336) 462-1080 or book a free estimate.
