How To Connect Two Faucet Supply Lines: A Detailed Guide


Whether you want your washing machine or dishwasher to receive both cold and hot water, you’ll have to figure out how to connect two faucet supply lines together. You may also want to make a connection if one of the supply lines is too short, and you have to add an extension.

Regardless of your purpose, the easiest way to connect two faucet supply lines is with a compression fitting. All you have to do is insert the end of each line into the fitting and twist. But you’ll have to ensure the fitting you have matches the type of line.

5 Types of Faucet Supply Lines

There are several types of faucet supply line tubes, and not all use the same compression fittings. Thus, you should find out what lines you have before starting the project. Here are the most common types.

Braided Nylon Flex Tubes

Braised nylon flex tubes are rarely used for kitchen and bathroom fixtures. These tubes are made of a PVC core reinforced with a braided outer core. You’ll likely see these tubes in gardens, garages, and other places where there is only cold water supplied.

The main reason you don’t find them in the house is that hot water can damage the nylon structure, leading to cracks or collapses. If you do have braided nylon tubes, it is a good idea to inspect them periodically or replace them with a higher-quality option.

On the bright side, these tubes are cheap, easy to find in all home improvement stores, and easy to install.

Stainless Steel Braided Flex Tubes

Stainless steel braided flex tubes are similar to nylon ones. The main difference is that the PVC core is covered with braided stainless steel.

The metal enhances the tube’s resistance and flexibility. Like braided nylon tubes, these lines are inexpensive and often used for both cold and hot water lines. While they can break easier compared to copper tubes, they are very easy to replace.

Polymer-Coated Flex Tubes

Another line type with a PVC core, polymer-coated flex tubes look a lot like stainless steel and work well for cold and hot water alike. They are very effective and more resistant to corrosion compared to any metal tube.

Another advantage of polymer-coated tubes is that you can bend and flex them easily – an excellent choice for most offset connections.

PVC Flex Tubes

PVC flex tubes are simple tubes that only have a PVC core coated with a thinner vinyl layer. They are similar to braided nylon tubes but don’t have the reinforced outer layer. Thus, hot water is even more likely to damage them.

Although inexpensive, PVC tubes are only recommended for cold water applications. If you want to run both hot and cold water through the tubes, choose a more resistant type.

Flexible Copper Supply Tubes

Lastly, flexible copper supply lines are the ones you can see in most kitchens and baths. They are often combined with polymer-coated or braided stainless steel tubes – the former typically used for rough-in plumbing and the latter for the connections to the fixtures.

Copper tubes are incredibly resistant to rust and corrosion. They are generally harder to install, requiring soldering, but will last for a long time.

How To Connect Water Supply Lines With Compression Fittings

We mentioned above that the easiest way to connect two water supply lines together is with compression fittings. Before getting started, you should measure the diameter of your tubes and buy appropriate fittings.

Some connectors will only work with specific tube types, so consider this as well when buying. To connect the lines, all you have to do is to insert each end into the fitting and fasten the connector. While the project is easy enough for beginners, you might want to follow the steps below to avoid mistakes.

Connecting Two Faucet Supply Lines in 5 Easy Steps

Plumbing projects can seem intimidating, but connecting two faucet supply lines together is truly child’s play. Here’s how to do it.

Things You Will Need

  • Compression fitting
  • Water line (if necessary)
  • Adjustable wrench or pliers
  • Protective equipment
  • Bucket
  • Teflon tape

Step 1 – Turn off the water and drain the line

To prevent a flood, you must turn off the water before working on supply lines and drain them in a bucket. Turn off the water at the main and place a bucket under the supply lines. Detach them from the faucet and drain them into a bucket.

Step 2 – Label the supply lines

Identify the supply lines and label them as hot and cold. This will make it easier to add new connection lines if needed.

Step 3 – Install your faucet

Connect the supply line to the faucet using the appropriate fastener (depending on the type of faucet). You might have to use a basin wrench at this stage.

Step 4 – Connect the lines with a compression fitting

There are two ways to connect the water supply lines, depending on the types of tubes you have.

For PVC or braided stainless steel tubes, wrap the end of the tube in several layers of Teflon tape and insert it into the threaded end of the connector. You can then attach the other side of the compression fitting to the supply line coming from the wall.

If you have a copper or other rigid pipe, position and bend the pipes as needed to align them, then insert each end into the fitting and tighten the fasteners.

Use the same method to add a new length of line to an existing pipe or to join the hot and cold supply lines before connecting them to an appliance.

Step 5 – Turn on the water and check for leaks

Once you’ve connected all loose ends, turn on the water and let it run for at least 10 minutes. Pat the connections with your hands to check for leaks. If all is well, you can start using your sink again.

Faucet Supply Line Won’t Fit: Here’s What To Do

The method above works great with standard water supply lines, but if your line has a larger or smaller diameter, you may find it hard to find the right compression fitting. If this happens, you can still connect the two lines by soldering them together.

  1. Check the fittings you want to use and make sure they fit snugly around the new pipe. If they do, put on your protective equipment.
  2. Sand the area with sandpaper or emery cloth to ensure a tighter grip for the solder.
  3. Brush both sides to be soldered with flux and place the fitting onto the pipe. Push to ensure a good grip.
  4. Light the soldering torch and wait for it to heat up. Start heating the metal from the bottom with a back and forth motion to prevent overheating.
  5. Apply the solder and let the torch melt it by holding both the solder and the torch firm. The capillary action will draw the solder into the empty space between the fitting and the pipe. Work your way around the fitting until the entire area is soldered.
  6. Turn off your torch and let the supply line cool off completely before moving it.

FAQs: Answers You Should Know

Connecting two faucet supply lines may not be hard, but you could still have questions. Check out the answers below.

How tight should water supply lines be?

Contrary to popular belief, water supply lines don’t have to be super-tight. The Teflon tape and O-rings in the fittings do a good job at providing a watertight seal even when the lines are only hand-tight. In fact, overtightening can damage the rubber seals or Teflon tape, leading to leaks.

Do you need Teflon tape on water supply lines?

Teflon tape is commonly used to seal water supply lines, especially when using threaded fittings and connectors. However, there are other options too. For instance, you could use pipe sealant. Moreover, some lines and connectors come with built-in gaskets that remove the need for using Teflon tape altogether.

Can you solder a pipe with water in it?

No. The water inside the pipe will prevent the copper line from getting hot enough to melt the solder. Even if the solder melts, the joint will most likely be too weak to hold on, and it could even start to leak as soon as you turn the water on. Always dry the pipes before soldering them.

Which pipe is best for the water supply?

Galvanized metal and copper pipes are the best choices for water supply lines. These pipes are more rigid than PVC or nylon yet still flexible. They’re more durable and easier to connect together with other lines if needed. Moreover, hot water is less likely to damage them.

To Sum Up

Connecting two faucet supply lines is an excellent project for beginner DIYers and homeowners who don’t want to call in a plumber. With few materials and tools, you can connect the lines in no time.

Have you ever done any type of plumbing before? Do you have tips or further questions? Leave us a comment.

Recent Posts