Water hammer in plumbing is when you hear a loud bang or knock in your pipes after you shut off a faucet or an appliance. That sudden stop results in a shockwave, and that’s the noise you hear. It’s basically the water smacking into the pipe walls. Let’s find out what causes a water hammer in the pipes, and is there a way to fix this issue?
Why Do I Suddenly Get a Water Hammer? 7 Common Reasons
Sudden Valve Shutoff
When water is flowing through your pipes and a valve shuts instantly, the flow does not slow down gently.
To explain it to you in layman’s terms, think of water moving quickly in your pipe like a train. If you close the faucet or the appliance suddenly, it stops all at once, and since the pressure has no space to spread out, it hits hard against the valve and the pipe walls.
That stop sends a shock back through the pipe. That sudden hit is what creates the hammering sound you hear.
High Water Pressure
If the water in your home is under too much pressure, it is always pushing harder than it should. When that pressure is cut off suddenly, the force is much stronger than normal. This makes the water hammer sound louder and maybe rougher. As time passes by, this strong pressure stresses the joints and fittings in your plumbing.
Loose or Unsecured Pipes
Plumbing pipes are supposed to be held in place tightly. If they are not, they will move every time the shock from water hammer runs through them. The more movement there is, the louder the banging gets, and it can possibly damage the pipe, which may cost you a lot in repairs.
Appliances with Quick-Closing Valves
Some appliances, like a dishwasher or a washing machine in your home, shut their valves very quickly. Unlike a faucet that you turn by hand, these valves close almost instantly.
That quick shutoff causes the water flow to stop at once, which creates the hammer effect. Because these machines run often, you may hear the water hammer noise many times in a single day.
Air Chambers or Arrestors Not Working
Plumbing systems often have air chambers or water hammer arrestors that are meant to absorb the shock of a sudden stop in water flow. If these are missing, filled with water, or not functioning, then there is nothing to cushion the force. The shock then runs freely through your pipes, which is another reason you hear the hammering sound.
Air Trapped In Pipes
Sometimes, you got air pockets in your plumbing. Instead of the pipe being filled smoothly with water, there are sections where air gets stuck. When the water rushes through the pipe and hits those air pockets, it results in a sudden jolt that shakes the pipe. That trapped air has no other way to escape, so it rattles around, and you hear the banging noise.
Ball-Float Valves
Ball-float valves, which are in your toilet tanks and open water tanks, like the ones on rooftops or storage tanks, can also trigger water hammer. It is possible that the tank fills and the ball float valve closes quickly, and the water has no time to slow down before hitting the stop. That sharp cutoff sends vibrations back through the pipe and creates the hammering sound.
How Do I Stop My Water Pipes from Hammering?
Now you know what causes water hammer in your plumbing pipes, so it is time to show you the fixes to stop these noises.
Install Water Hammer Arrestors
The easiest fix is to train yourself to turn taps off slowly, not in one sudden twist. That alone cuts down the shock. But for appliances that shut valves instantly, like dishwashers or washing machines, you can’t control how they close.
For these, the best solution is to add mini water hammer arrestors directly on the supply hoses of the appliance. They’re small, inexpensive, and manufactured exactly for this problem. You just have to screw them onto the water line behind your washer or dishwasher, and they act like a cushion every time the valve shuts. When the water stops suddenly, the arrestor absorbs the shock so it doesn’t slam back into your pipes.
Add a Pressure-Reducing Valve
If the water pressure is too high in your plumbing, you or a plumber can test it with a gauge, and if it’s over the recommended level (usually around 40–60 psi for homes), you need a pressure-reducing valve installed on your main line.
This valve lowers the incoming pressure from the city supply to a safe level. Once that’s in place, the pipes don’t get slammed so hard, and the water hammer noise eases off or is gone for good. High pressure is one of the biggest culprits, and fixing it also saves wear on your plumbing fixtures in general.
Secure Loose Pipes
Another fix is to fasten the pipes securely with brackets, clamps, or pipe straps so they can’t jump around. But this is great for exposed plumbing. But the piping behind walls needs the help of a plumber for a partial teardown. The good news is that with this fix, the shock still happens inside the pipe, but the pipe itself no longer bangs around. That takes away a lot of the noise.
Reset or Install Air Chambers
If you already have air chambers in your plumbing, they might be filled with water instead of air. To reset them, you can shut off the main supply, drain all the water from the pipes by opening every tap in your house, and then close everything before turning the water back on. That lets air back into the chambers so they can do their job again.
This bleed is great for the trapped air in your pipes, as well as water flow pushes out the trapped air, and your pipes settle back to normal. It’s a simple process, but very effective if air pockets are the issue.
In case your plumbing doesn’t have air chambers, or if this draining trick doesn’t work, the long-term fix here is either to install the air chambers or, again, water hammer arrestors that don’t lose their air cushion.
Replace Old Ball-Float Valves
Ball-float valves, whether in toilets or in open storage tanks, can also cause hammering when they shut too abruptly. The fix here is to replace them with modern slow-shut float valves. These are designed to close gradually, which means the water flow doesn’t stop in a single snap.
That slower shutoff gives the water time to settle instead of slamming against the valve. If you’ve got an old-style ball float in your tank, swap it out for a slow-shut type for a solid long-term solution.
Conclusion
So, now you know what water hammer really is, why it happens in your home plumbing, and what the practical fixes that actually work are, like arrestors, pressure regulators, pipe straps, and slow-closing valves.
Dealing with water hammer isn’t just about silencing the noise; it’s about protecting your pipes from long-term damage, too. If you’re unsure what’s causing it in your home or you want a lasting fix, you don’t have to figure it out on your own. California Coast Plumbers have the expertise to pinpoint the real cause and fix it once and for all. Reach out today and get your plumbing running the way it should.