Troubleshooting and Repairing a Toilet Water Supply Line Leak

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Nobody wants to deal with a leak anywhere in their homes but even less so when that leak is around the toilet.

If you’ve noticed water at the base of your toilet, it’s possible you’ve got a leak somewhere along the toilet supply line. And while we don’t do repairs like this at In-House Plumbing Company (we specialize in the more of the non-DIY repair like underslab leaks), we can let you know how to do it.

Because believe it or not, this is a fairly simple repair that you can do yourself in less than an hour.

Find the Leak

The first step with any leak is not a surprising one: Find it!

The toilet supply line is attached to a cold fresh water pipe under the slab or in the wall to the toilet tank.

The water from the cold line runs through the supply line to fill the tank which then fills the bowl after you flush the toilet.

As I’ve mentioned in previous posts, there is always pressurized water in your water pipes. This is also the case with the toilet supply line. It is the fill valve in the tank that stops it from continually pumping water into the tank.

So if there is a leak along the line, there will be a consistent drip making it a little easier to figure out where the problem might be.

The leak could be in the line itself or from the fill valve fitting at the tank or the shut off valve fitting where the supply line connects to the fresh water line.

Loose Toilet Supply Line Valve Fittings?

It’s always good to rule out the simple stuff first. So before I go on with how to repair your supply line leak, if the leak is coming from one of the valves, make sure the fittings aren’t loose.

If your home or toilet line is newer, it’s possible the valves are OK and just need to be tightened.

But if the fittings are plastic, be careful not to tighten them too much because you could break them. (It might be worth it to go ahead and replace the valves with a metal fitting or a reinforced plastic compression fitting even if it is just a loose valve. Some of the cheaper plastic fittings break too easily.)

Use a pair of pliers to tighten the fittings enough to stop the leak — hand tightening usually isn’t enough to keep it from leaking. Then once the rubber gasket has had a few hours to compress, tighten it just a little more.

If this does not solve your leak problem, it’s time for the next step.

Check the Washers and Threads

A leak can also be because of worn out washers and/or threads.

Turn off the water at the shut off valve and remove the hose. Remember, there will be water in the hose so have something like a small Tupperware or bucket to catch it.

If the washers look worn or are cracked, replace them. Also check to see if the threads are stripped. If so, you can wrap pipe leak tape — also referred to as plumber’s tape — around the threads to create a seal.

Put everything back, dry everything off with a towel, and turn the water back on. If the leak has stopped, you’re done! If not, it’s time to go ahead and replace the line.

Replace Toilet Water Supply Line

If you’ve tried everything above and the leak has not stopped, you need to replace the supply line. Of course, you can always just go ahead and replace the line from the start and skip the step checking the washers and threads. A new one will only run you around $10 so if you’re looking to save time, you won’t be out too much money.

Tools You Need:

  • Crescent wrench
  • Bucket or container to catch water from disconnected line
  • A towel
  • The new line
  • First turn off the water at the shut off valve.

Use the crescent wrench to loosen the fittings at both ends of the hose and remove the old hose. Watch out for the water in the hose. Use the container you got to catch the water.

Reattach the new hose, dry everything off, and turn the water back on.

Flush the toilet and make sure everything looks ok, no leaks at the fittings or along the line.

And that’s it!

If the leak came from the supply line and/or it’s fittings, you are done for the day.

The Leak at the Toilet is Not Gone!

If you’ve tried everything you can with the toilet supply line and there’s still a leak, it’s something else.

In this case, it might be time to call someone in for help.

While we don’t typically do these kinds of repairs, give us a call at 972-494-1750 or email We can help you decide what your next steps should be.



In-House Plumbing Company

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