The cause of low water pressure varies depending on whether the pressure is low throughout the house or isolated to specific fixtures. Whole-house causes include the main water shut-off valve and the pressure regulator. Common causes with fixtures include clogged aerators and hard-water deposits.
A partially opened main shut-off valve is often the cause of low water pressure throughout the entire home. The valve is normally located at the front of the house. Turn it fully counter-clockwise or parallel to the pipe, depending on the type of valve, to ensure adequate pressure to all pipes. A failed pressure regulator could also cause low pressure. In this case, call out a qualified professional for replacement.
If the low water pressure is affecting a shower head, accumulation of hard-water deposits often restricts the flow of water. Test the water pressure with the shower head removed to determine if cleaning or replacement is required.
Clogged aerators sometimes cause low pressure in faucets. Remove the aerator and turn the faucet on to determine if the aerator is the problem. If the faucet still has low pressure, the problem could be in the fixture or in the lines leading to it. To test the faucet, turn off the water to the fixture, remove the lines, and turn the water back on to isolate the problem.