How to Replace Compression Fitting Water Supply Lines


Some water supply lines are secured together by compression fittings. A compression fitting is made up of two threaded ends, two screw-on nuts that attach the water line to the fitting and the ferrules that seat the water line inside of the compression fitting. If a water supply line is broken or is in need of replacement, the compression fittings must be removed from the water line in order to replace it. Make sure the new fittings are installed correctly to the water lines to prevent them from leaking.

Things You'll Need

  • 2 adjustable wrenches
  • New water supply line
  • Water line cutters
  • New compression fittings
  • Teflon tape
  • Locate the water supply valve to the water supply lines in need of replacement. Shut off the water supply valve by turning the handle closed with your hand or an adjustable wrench. Turn a couple of faucets on inside of the house to release the water pressure from the water supply lines. Close the faucets when the water stops flowing out of them.

  • Locate the compression fitting that secures the end of the water line that needs replacing. Loosen the nuts from the compression fitting with two adjustable wrenches. Position one of the adjustable wrenches onto one nut and the other wrench onto the other nut. Turn the nuts counterclockwise to loosen them from the compression fitting, then remove the wrenches and finish unscrewing each nut by hand until they are completely free of the fitting.

  • Pull each end of the water line out of the compression fittings. Remove additional compression fittings, if needed, by repeating this process. Pull the old water supply line out and position the new water supply line in its place. Make sure the new supply line is the same size and configuration so it can readily accept the compression fittings.

  • Add compression fittings to the ends of the water supply lines where needed. Push the screw-on nuts onto the ends of each water line. Make sure that the threads of the screw-on nuts are facing the ends of the water lines. Slide the screw-on nuts about four or five inches up on the water lines.

  • Slide the compression fitting ferrules onto the ends of each water line, pushing them about one inch past the ends. Use the flaring tool to cut off the excess water lines that are sticking out of each ferrule. This also secures the ferrules to the ends of each water line. Push the ends of both water lines into the mating compression fittings until each ferrule is seated inside the mating compression fitting.

  • Wrap Teflon tape clockwise around the threaded ends of the compression fittings. Push the nuts back along the supply lines and screw them onto the ends of the compression fittings until tight. Finish tightening the nuts with the adjustable wrenches. Check the connection of the compression fittings to the water supply line by gently pulling on the ends of the water lines.

  • Move to the next section of the water supply line that requires a compression fitting and repeat the steps as outlined above until the water line is completely hooked up. Turn the water supply valve back on and inspect the new water supply line at the compression fittings for leaks. If none are present, leave the water on. If leaks are present, turn the water off, tighten the fitting connection where the leak is and turn the water back on.

Tips & Warnings

  • The compression fittings are designed to join, splice and connect water lines.
  • Make sure that there is no excess water line sticking out of the end of a ferrule. The ferrules should be at the very end of each water line so they can properly seat to both ends of the compression fitting.
  • You can also use a metric open-end wrench set in the place of the adjustable wrenches if needed.
  • If the compression fittings are not installed properly to each end of the water line, they will leak.
  • Make sure all of the pressure is released from the water lines before removing the compression fittings.


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