How to permanently cap off a water supply pipe or line: Easy Steps

Permanently capping off the end of a water pipe can be a difficult task if you don’t use the right tools. It’s extremely important to seal off any openings in your water system, as well as make sure there are no leaks in the pipe. However, it’s also easy to make a mistake, which can cause water damage and lead to a costly repair. If you’re in this situation, here’s how to cap off a water pipe.


Decide where to cap off the water supply pipe

The first step to sealing off a water pipe is to decide where you’d like the pipe to end. You also have to know the diameter of this pipe so that you can get the right material.

Turn off the water before you start working on your system. This is often done by closing a valve in your pipes. If you don’t have one for the room itself, you might have to close the main valve. Open up the faucets to drain water out of your pipes. Also, get buckets and towels ready as pipes can contain a lot of water. This can lead to damage if you are not careful.

Choose a cap that’s compatible with your pipe

 Homes generally use copper, PEX or steel pipes. PEX is a type of plastic and you will feel it when you touch this pipe. Copper pipes have a red color. Steel pipes are often grey. 

To cap off a steel pipe, you will have to create a thread on it. This is generally done with a machine (and some oil). Don’t forget to use a calibration tool before you do this. Once this is done, you can use teflon tape to make sure that the end cap fits tightly. There are also systems that allow you to press the cap over the pipe. You can often rent these in a hardware store.

To add a stop to a copper pipe, you will have to cut off the pipe in the desired length. Then you are going to clean the pipe with a knife and some steel wool. The final step is to add the cap. Often you have to use a tool to tighten this. It is also possible that you have to solder it.  Check your local code to see what is needed. You can also use a Sharkbite for copper. This is quite easy to use as you just have to slide it over the pipe and check if the connection is tight. Some plumbers don’t like Sharkbite but they tend to hold up quite well. 

Adding an end cap to a PEX pipe can be quite straightforward. If you have a PEX system, you can use a Sharkbite. This just needs to get pushed on the pipe and you are good to go. You can see when it is installed properly as 

 PEX-A systems also have special end caps but these need to be installed differently. You have to use the expanding tool to slide the fitting inside the pipe. 

PEX-B systems use a ring that slides over the fitting. This ring is then tightened with a cinch clamp tool. This is quite similar to installing a normal fitting. Instead of connecting two pipes, it is just ending one. Make sure to get the right end cap as the ones that work for PEX-B don’t always work for PEX-A and vice versa. You also need to get one for the diameter of the pipe that you have. 

 End caps are cheap and make a secure connection. Pipe sealers or chemical ways to close the pipe are not that often used by plumbers as they can break down over time. For this reason, they are not used by professional plumbers.

Test your installation

The final step is to open up the valve again and see if you have leaks. A water pressure test is recommended before doing this. Check your local code to make sure that everything is according to their requirements. 

 It is also important to keep in mind that your pipes shouldn’t have dead ends with standing water. Standing water can become dirty. If the pipe is still connected to your manifold, it can spread over your whole system. This can lead to a lot of problems as this can spread dangerous substances and break your plumbing system and be dangerous for the inhabitants. For this reason, standing water should be avoided in a plumbing system.

It can be a better idea to remove a pipe if you don’t use it anymore. This can easily be done at the manifold. You can close the valve for this pipe if there is one. If there isn’t one, you will have to add an end cap on this part of the manifold so that water doesn’t leak there. Copper and steel systems often don’t have a manifold and then you will have to remove a fitting. 

If you are working with a gas pipe, you might have to use another approach, this article only discusses water pipes. 


 Sealing off a pipe is quite straightforward if you have the right tools. Make sure to clean the pipe before adding the end cap. You have to use the right end cap for your system and the type of material that you have. Sharkbites have made this process a lot easier as you can often slide them over a pipe. Other approaches can be stronger but can require special tools. 

End caps are pieces of metal that slide over the end of the pipe. They are cheap and easy to install. Just make sure that you get the right ones for your system. The type of material and the diameter are things that you have to check. Plumbers generally don’t use chemical ways to close pipes as this can break down over time. Given that end caps are so cheap, there are not a lot of reasons to use chemical ways to close the pipe. 

When you cap off a pipe, you should also take the water quality in the rest of the system into account. If water is standing still in a part of the water supply line, it can affect the water quality in the rest of your system. This can even lead to dangerous situations as bacteria can build up and spread. For this reason, it is important to make sure that you only cap off a water pipe in a part that doesn’t affect the rest.