Last reviewed and updated: 2026-09-24
A sudden loss of water pressure across the whole house usually means water is escaping before it reaches your fixtures, a valve has partly closed or failed, or the utility is working on the main. If the drop is confined to one fixture it is almost always a blocked aerator or cartridge. Check with a neighbor first: if their pressure dropped too, it is the utility, not your plumbing.
A sudden drop usually means volume is being lost before it reaches the fixtures, most often at the buried service line or in corroded older supply pipe.
Narrow it down
- One fixture or the whole house? One fixture means a blocked aerator, cartridge or supply stop. The whole house means something upstream.
- Hot side, cold side or both? Hot only points to the water heater or a hot-side leak. Both points to the main supply.
- Ask a neighbor. If their pressure dropped at the same time, it is the utility main and nothing to do with your plumbing.
- Check the valves. The main shut-off and the meter valve are sometimes left partly closed after other work.
- Read the static pressure. A gauge on an outside tap costs very little. Normal is roughly 40-80 psi; a low reading points upstream and a high reading is its own problem.
- Run the meter test. Pressure loss plus a turning meter with everything off is a leak losing volume before it reaches the house.
The usual causes
| Cause | Pattern | Fix |
|---|---|---|
| Service line leak | Whole house, plus a turning meter and possibly a soggy lawn | Locate and repair or replace the line |
| Failed pressure-reducing valve | Whole house, sudden, gauge reads low or erratic | Replace the PRV |
| Partly closed main or meter valve | Whole house, often right after other plumbing work | Open the valve fully |
| Utility main work or a break | Whole neighborhood at the same time | Nothing: the utility restores it |
| Blocked aerator or cartridge | One fixture only | Clean or replace |
| Water heater fault or sediment | Hot side only | Service or flush the heater |
| Corroded galvanized pipe | Gradual over years, not sudden | Repipe |
| Slab or wall leak | Whole house, with running water sound or damp | Detection and repair |
Pressure loss plus a high bill is a strong leak signal. Either on its own has innocent explanations. Together they mean water is going somewhere before it reaches your taps, and it is being metered on the way.
Frequently asked questions
Why did my water pressure suddenly drop?
Usually water escaping before it reaches your fixtures, a valve that has partly closed or failed, or utility work on the main. Check with a neighbor first, if their pressure dropped too, it is the utility rather than your plumbing.
Is low water pressure a sign of a leak?
It can be, particularly if the whole house is affected and the water meter turns with everything off. A large leak diverts volume before it reaches the fixtures. Low pressure combined with a rising water bill is a strong indicator.
Only one tap has low pressure. What is that?
Almost always local to that fixture, a blocked aerator, a worn cartridge, or a supply stop not fully open. Clean the aerator first; it resolves most cases.
What is normal water pressure?
Roughly 40 to 80 psi for a residential supply. A gauge that screws onto an outside tap costs very little and takes a minute to read. Above about 80 psi is its own problem: it shortens the life of supply lines, water heaters and appliance hoses.
Only the hot water pressure dropped. Why?
That points to the water heater or the hot side of the system, sediment build-up, a failing dip tube, a partly closed heater valve, or a leak on the hot run. In a slab home, a hot-side leak often comes with a warm patch on the floor.