What Is Water Hammer?
Water hammer is the banging or knocking noise in pipes when a valve or appliance shuts off water flow abruptly. Moving water has momentum, and when it is stopped suddenly, the resulting pressure surge travels back through the system as a shock wave. Repeated shocks loosen joints, damage fixtures, and can eventually cause leaks.
What causes it
The most common triggers are appliances with fast-acting solenoid valves: washing machines, dishwashers, and ice makers close in milliseconds rather than the gradual closure of a hand-operated tap.
The problem is worse when water pressure is high, when pipes are inadequately secured so they can move, and when the air chambers originally installed to absorb shock have filled with water, which happens over time.
Fixing it
Three measures address it, roughly in order of how often they are the answer.
- Check and reduce water pressure. High pressure amplifies every shock, and a PRV frequently solves water hammer as a side effect
- Install water hammer arrestors near the offending appliance, which contain a sealed air chamber that cannot waterlog
- Secure loose pipes with proper strapping so they cannot move and amplify the noise
- Draining the system can temporarily restore old-style air chambers, though they refill over time
Frequently asked questions
Is water hammer actually damaging?
Yes, cumulatively. Each shock stresses joints, fittings, and fixture internals. Over years it loosens connections and contributes to leaks that appear unrelated. It is also a reliable indicator of high water pressure, which is doing its own separate damage throughout the system.
Why did it start suddenly?
Usually either a new appliance with a fast-closing valve, a change in municipal supply pressure, or old air chambers finally waterlogging. Testing your water pressure is the cheapest first diagnostic and frequently identifies the cause.
See also
Related services
- Emergency Fixture Repair and InstallationRepair and replacement of faucets, shutoff valves, supply lines, garbage disposals, and other fixtures, including failed connections that leak.
- Whole-House RepipingReplacement of a home's supply piping where the existing system has reached end of life, using PEX or copper.
- Emergency Leak DetectionNon-invasive location of hidden water leaks behind walls, under floors, and beneath slabs using acoustic, thermal, and pressure testing equipment.