Short answer
Low water pressure after turning the water back on is usually caused by trapped air, partially closed shutoff valves, or clogged faucet aerators. The issue is often temporary and can be fixed with a few simple checks.
Why this happens
When water is shut off, air enters the plumbing system. When the supply is restored, that air can:
- Restrict water flow
- Push debris into faucet aerators
- Cause valves to reopen unevenly
If the water was turned on too quickly, pressure problems are more likely. That’s why restoring water slowly — as explained in how to turn water back on after shutting it off safely — is important.
Step-by-step: what to do
- Check the main shutoff valve
- Make sure it is fully open
- Wheel-style valves should be turned counterclockwise until they stop
- Lever-style valves should be parallel with the pipe
- Check individual fixture shutoff valves
- Look under sinks and behind toilets
- Ensure they are fully open
- Run faucets to clear air
- Start with the lowest faucet in the house
- Let it run until water flows steadily
- Work your way up to higher fixtures
- Clean faucet aerators
- Unscrew the aerator at the tip of the faucet
- Rinse out debris or sediment
- Reinstall and test water flow
- Check outdoor spigots
- Outdoor faucets often collect debris after shutoffs
- Run them briefly to clear trapped air
What not to do
- Don’t assume low pressure means a major plumbing failure
- Don’t open the main valve further if it’s already fully open
- Don’t ignore one fixture working poorly while others are fine
- Don’t call a plumber before checking aerators and valves
When to call a professional
Call a plumber if:
- Water pressure stays low for more than a few hours
- Only one area of the house is affected and cleaning doesn’t help
- Pipes vibrate or make loud noises
- Pressure suddenly drops again after returning to normal
These can indicate valve damage, internal pipe issues, or pressure regulator problems.
Safety notes
- Turn water on slowly in older homes
- Be cautious around appliances connected to water lines
- Watch for leaks while testing pressure
Frequently asked questions
Why is only one faucet low pressure?
Usually a clogged aerator or partially closed fixture valve.
Can air in pipes cause low pressure?
Yes. Air pockets restrict flow and usually clear after running faucets.
Will low pressure fix itself?
Often yes, especially within the first hour after restoring water.