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Plain-English article
Low Water Pressure in Thornton, CO: Causes and Fixes
Weak flow is annoying, and it can also be a warning. The first question is whether it is one fixture or the whole house, because that splits the causes into two groups.
By the Thornton Plumbing Co. team ·
One fixture or the whole house
If only one faucet or showerhead is weak, the problem is local. If every tap is weak, look at the main valve, the pressure regulator, the service line or the city supply.
Test with a pressure gauge on a hose bib. Many homes run between 50 and 70 psi. Anything far below that deserves a look.
Local causes
A clogged aerator at a faucet is the most common cause of weak flow. Unscrew it, soak it in vinegar and rinse. Showerheads clog with scale in the same way.
A partly closed stop valve below a sink or behind a toilet limits flow. A kinked supply line, a clogged cartridge and a worn valve also cause trouble.
Whole-house causes
A main shutoff that is only partly open cuts flow to the whole house. After a repair or a spring hydrant flush, check that it is open. A pressure regulator that fails reduces the supply or lets it surge.
A leak in the service line also reduces pressure. Check the yard for wet spots, and see the water line page.
Where to look first
Start with how widespread the problem is.
| Where it shows | Likely cause | First step |
|---|---|---|
| One faucet or shower | Clogged aerator or showerhead | Soak it in vinegar |
| Hot side only | Heater sediment or a valve | Check the heater shutoff |
| Every tap | Main valve, regulator or service line | Test pressure at a hose bib |
| Rusty water too | Corroded pipe | Ask about a pipe inspection |
Corroded pipe
Old galvanized pipe narrows from the inside as rust builds up. Flow drops and rusty water appears, especially at the start of the day. The answer is often a repipe, covered under repiping.
Hard water scale also coats pipe walls. A softener helps going forward.
Water heater and filters
If the problem is only on the hot side, the water heater may be clogged with sediment, or a valve may be partly closed. Flush the tank and check the shutoff.
A whole-house filter with a dirty cartridge reduces flow. Replace the cartridge on schedule. A softener bypass left half open can also cause trouble.
City supply and seasons
Sometimes the pressure drops because of city work or a main break. Ask neighbors, and check the city's notices. During spring hydrant flushing, which runs for about five weeks, pressure may change for a short time.
In summer, high demand can reduce pressure at peak hours. If the dip is brief and regular, it is probably not a problem in your house.
Start by sorting the symptoms
Low pressure at one fixture is a local problem, often a gritty aerator or a stop valve left partway shut beneath the sink. Low pressure at every tap points to the supply side: the main shutoff, a pressure regulator, a service line or the city main. Low pressure on the hot side alone points to the water heater or its lines.
Test at an outdoor spigot as well. Weak flow there too suggests the problem sits before the branches that feed your fixtures.
Checks you can do without tools
Make sure the main valve is fully open. A gate valve that was nudged during other work can sit half closed. Unscrew a faucet aerator and rinse out grit and scale, which is common with hard water. Run each shower with the head removed to see whether the head or the pipe is at fault.
If you have a gauge that threads onto a hose spigot, a reading below about 40 psi suggests a supply problem, and a reading above 80 psi suggests the opposite problem, which damages fixtures. Static pressure is read with everything off.
Regulators, service lines and the street
Many houses have a pressure reducing valve near the main. When one fails, pressure can drop or swing. They wear out, and a plumber can test and replace one. Galvanized pipe loses diameter inside as mineral buildup narrows it, which is why older homes with that material often lose pressure over the years. That is one reason people look at repiping.
A fault in the buried pipe linking meter and house can also drop pressure, sometimes with a wet patch in the yard. Call 811 before anyone digs. See water line repair and replacement for what that repair involves. If the whole street has weak flow, call the city, since the cause may be the main, or a hydrant flushing event in spring.
When to call
Call if pressure drops suddenly, if you see water where it should not be, or if the meter spins with everything off. Those point toward a leak, and a leak is better found early. The guide on leak detection explains the usual methods.
Ask the city before you spend money
Pressure in the street can dip during a main break, heavy fire flow or maintenance work. Thornton's spring hydrant flushing program, which runs for about five weeks, can briefly change pressure and stir up sediment in nearby lines. If low pressure begins on that schedule and clears in a few hours, run a cold tap for a few minutes and then check the aerators for grit.
If your neighbors have the same trouble, call the city's utilities line and tell them before paying a plumber. If only your house is affected, the cause is on your side of the meter.
Pipe material and age
Galvanized steel, found in some older houses, narrows inside as it ages. Copper with scale or a partly collapsed section can restrict flow as well. If low pressure has worsened slowly over the years and every fixture is affected, the pipe itself is a leading suspect.
Quick answers
Asked about low pressure
Many homes run between 50 and 70 psi. A gauge on a hose bib shows yours.
Scale in the showerhead is the usual cause. Soak it in vinegar.
Yes. A service line leak reduces pressure at the house.
If pressure is low at every tap, or you see rusty water, call.
Connected services
Repiping & Whole-Home Pipe Replacement
Retire worn galvanized, copper or polybutylene supply pipe with new lines across the whole house. Open page
Faucet & Sink Repair
Quiet a dripping tap, bring back full flow and swap out seized stop valves and outdoor spigots. Open page
Related reading
Water hammer: the banging pipes
A bang in the wall when a tap or washer shuts off is water hammer. Here is what causes it and which fixes work. Open page
PEX vs copper pipe
Both work. PEX is quick and flexible, copper has a long record. Here is how hard water, freezing and cost shape the choice. Open page
Tracking down a hidden leak
Reading the meter, dyeing the toilet tank and walking each room will turn up most leaks. Here is the order to do them in. Open page
Pressure dropped at every tap?
Phone in and say whether the drop hits hot, cold or both.