Why does my water pressure fluctuate?

Fluctuating water pressure is often caused by a failing pressure regulating valve, which stabilizes incoming water pressure from the municipal supply. Other causes include air trapped in pipes, sediment in the water heater or pipes, or multiple fixtures running simultaneously. Check if the fluctuation happens with all fixtures or just one. If it is throughout the house, the pressure regulator may need adjustment or replacement. A water hammer arrestor can help stabilize pressure from quick-closing valves on appliances.