Just one fixture
Unscrew the aerator at the tip of the faucet or remove the showerhead, and soak it in vinegar to dissolve mineral build-up. If the pressure comes back with the aerator off, that was the problem.
Only the hot water
If cold water is strong but hot is weak, the water heater's shutoff valve may be partly closed, or sediment may be restricting the tank's outlet. A plumber can flush the tank and check the valves.
The whole house
- Make sure the main shutoff valve is fully open, especially after recent plumbing work.
- Many homes have a pressure regulator where the water line enters. When they fail, pressure drops or swings.
- A leak can steal pressure. Check your water meter with everything off; if it moves, you may have a leak.
- Older galvanized steel pipes can corrode inside and narrow over time.
- Ask a neighbor. If they're weak too, call the water utility.