Narrow low water pressure down by pattern before you replace anything. If one fixture is weak, the cause is usually at that fixture: the aerator, showerhead, stop valve or cartridge. If only hot water is weak, look at the water heater and the hot side. If every fixture is weak, measure pressure at an outside hose bib with nothing running. That one reading tells you whether the house supply itself is low or something inside the house is restricting flow.
Three quick checks
- One fixture or many? Try a bathroom faucet, a shower and the kitchen sink.
- Hot vs cold. At the same weak fixture, compare hot and cold.
- Gauge at a hose bib. Screw a pressure gauge onto an exterior hose bib with all fixtures off for static pressure, then watch how far it drops while a fixture runs.
Static pressure is the no-flow reading. A house can read normal statically and still feel weak in use if something restricts flow.
Match the pattern to the likely cause
| What you notice | Likely area | First check | Call a plumber when |
|---|---|---|---|
| One sink or shower is weak | Aerator, showerhead, supply stop or cartridge | Remove the aerator or showerhead screen and look for grit or scale | The stop valve is seized or the cartridge won’t come out |
| Hot is weak, cold is fine | Water heater, mixing valve or hot branch | Compare hot and cold at the same fixture | The heater leaks, trips its safety devices, or flushes heavy sediment |
| Whole house is weak all the time | Main shutoff, pressure-reducing valve, utility supply or well system | Read static pressure at the hose bib | The reading is well below your home’s normal or swings sharply in use |
| Fine until several fixtures run | Flow restriction or a partly closed valve or filter | Run fixtures one at a time and compare | The drop is severe, or the house has older galvanized pipe |
| Normal outside, weak inside | Filter, softener, bypass valve or branch restriction | Check filter cartridges, bypass valves and branch shutoffs | The restriction is inside finished walls or a treatment tank |
What changes the answer
- Recent plumbing work. Debris from repairs often lands in aerators, showerheads and cartridge screens. Clean those first.
- Utility work nearby. Main flushing or repairs can stir up sediment and change pressure. If neighbors notice the same thing, call the water utility.
- Filters and softeners. A clogged cartridge or a half-open bypass restricts every fixture downstream.
- A well. Look at the pressure tank, the pressure switch and any whole-house filter before the fixtures. A pump that short-cycles, or a gauge that swings fast, is a job for a well or pump professional.
- A recent freeze. If one area went weak after a cold snap, a line may be frozen or split. Shut off the water and call a plumber before anything thaws in a wall.
Reading the gauge
There’s no single “low” number that diagnoses every house. Compare your reading with what the utility or well system normally supplies, and write a baseline reading near the main shutoff for future comparison. High pressure is the other side: the International Plumbing Code calls for a pressure-reducing valve where static pressure inside the building exceeds 80 psi, subject to the code your area has adopted. If your house has a regulator and pressure drifts up or down over time, see the regulator guide linked below.
When to skip DIY
Call a plumber when low pressure appears suddenly across the house along with leaks, rusty water, air in the lines or new water stains, or after a freeze. Those signs point past a clogged screen.
FAQ
How do you tell low water pressure from low flow?
Low water pressure shows up across several fixtures and reads low at a hose bib. Low flow shows a normal pressure reading but weak output at a specific faucet, shower, or branch line.
What PSI counts as low for a house?
There is no single low-pressure cutoff that diagnoses every home. Compare static and flowing readings with the utility or well-system baseline. Static pressure above 80 psi is where the International Plumbing Code calls for a pressure-reducing valve, subject to the locally adopted code.
Why is hot water weaker than cold water?
Hot-only weakness points to the water heater, a mixing valve, or a restriction in the hot branch line. Comparing hot and cold at the same fixture separates that quickly.
Should I call the water company or a plumber?
Call the water company when the street or neighborhood shows the same pressure drop. Call a plumber when the issue stays inside the house, the hose bib reads low, or the pressure-reducing valve looks suspect.
Related guides
Sources
This is a diagnostic sequence, not a substitute for a plumber’s inspection. Local code sets the pressure limits that apply to your house.