Toilet Leaking From Water Supply Line | Here’s The Fix

Diagnosing and fixing a water supply line leak can be a tad challenging. There are several reasons it could be leaking, so you will need to conduct some trial and error to find out why it is leaking. 

The good news is that you can fix the issue yourself without the help of a licensed plumber. Of course, if you aren’t an avid DIYer or you don’t feel comfortable making the repairs yourself, you can always call a plumber to fix the problem. If you want to make the repairs yourself, continue reading to learn how. 

What is a Toilet Water Supply Line

Toilets are rather simple in makeup – there isn’t much to them in terms of parts and how they work. If you aren’t familiar with toilet schematics, the water supply line is a chrome steel flex pipe or white-colored hose behind or underneath the toilet tank that goes from the water valve on the wall to the bottom of your toilet tank. This hose is fed by either PVC or copper pipe behind your walls or under the floors, which draws water flow from the main household water line.

the final section of the water supply leading to the tank
The final section of the water supply leading to the tank

Finding a Leak In The Water Supply Line

There are several reasons a toilet water supply line can leak. You must diagnose the issue to make the appropriate repairs that will resolve the problem. 

A water supply line leak can be a slow innocuous drip or as impactful as a sustained stream of water. This is largely determined by the water pressure and the size of the gap or crack in the pipeline. 

When inspecting the system and looking for visual evidence of the leak you may find a small puddle behind your toilet, or you may hear constant dripping either behind the wall or on the floor of your bathroom. You may even notice a reduction in water flow or water pressure when you flush the toilet. 

Check the water line that connects the toilet tank to the wall. Look for any signs of moisture, including water droplets, discoloration, or dampness. If you notice any of these signs, you can find the exact location of the leak by wrapping a piece of toilet paper around it. Check back periodically to see if the toilet paper is wet. If it is, you’ve found the location of the leak.

While a water supply line leak is often subtle but persistent, if left unresolved, the leak can cause damage to the floor and adjacent surfaces. Potentially leading to rot or mold setting in causing serious structural problems in the bathroom.

Water leak that has caused structural damage
A water leak that has caused structural damage

Once you have identified the problem, you can repair it yourself or call a plumber to do it. If you want to make the repairs yourself, read on. I’ll give you step-by-step instructions that will enable you to fix a leaky water supply line like a pro.

Repairing A Leaking Water Supply Line

Fixing a leaky water supply line is well within the capability of a competent DIY’er, but you will need some specific tools. 

Equipment Required

  • Pipe Wrench
  • Container To Catch Dripping Water
  • Old Towel For Drying Spills
  • Plumbers Tape
  • Rubber Washers 

Step 1: Locate the Leak

The first thing you need to do is figure out where the water is coming from. The leak might be easily visible, but if not, you can use a dry cloth to dry the water supply line and then run your finger down the length of it to see if you can feel where the leak is coming from. Or as I described earlier, you can wrap a piece of toilet paper around the area and check to see if it shows signs of wetness.

If the leak is coming from the water supply line itself, it probably has a crack in it. If this is the case, you will need to purchase a new water supply line to replace the cracked one, you can pick them up here at for under $15. If, on the other hand, the leak is coming from either end of the hose in or around the fittings, you will probably be able to repair the issue without needing to replace the entire hose. 

Replacement toilet supply line
Buy a replacement toilet supply line

Step 2: Shut Off the Water Supply

Locate the water supply valve (the water supply hose is connected to it at the wall behind your toilet) and turn it all the way clockwise. This will shut the water supply off to the toilet. To be on the safe side, you might also want to shut off the main water supply to your house, especially if you find out you need to replace the water supply hose entirely.

Step 3: Attempt To Tighten Connectors and Fittings

If you have determined the leak is coming from the fittings at either end of the water supply hose, you can try tightening them to see if that stops the leak.

Use a small pipe wrench to gently and slowly tighten the nuts that hold the water supply line in place. Don’t apply too much pressure as these nuts are sometimes made of plastic, which can be delicate. Once you have tightened the fittings, use a cloth to dry the area, turn the water back on, wait a few minutes, and then run your finger over the fitting/hose to see if the leak has stopped.

Step 4: Replace Rubber Washer

If the water supply line is still leaking, the rubber washers inside the fittings may be worn. You will need to turn the water off at the valve again, and this time, loosen and disconnect the fittings to reveal the rubber washers inside. 

You may or may not be able to see the wear and tear on the washers, but regardless of whether you can or not, you should replace them since you have the old ones out. 

After replacing the rubber washers, reattach the supply hose and turn the water back on. Wait a few minutes and then check for leaks. 

Note: The water supply line will still have water in it after you turn the water off. Use a bucket to place the end of the hose into once you have disconnected it to avoid spilling water on the floor. 

Step 5: Seal Threads with Plumber Tape and Tighten

If, after replacing the washers and tightening the fittings you still leak, it is time to break out the plumber’s tape. Plumber’s tape is used to create a watertight seal on threads. Over time, the plastic threads on the toilet fittings can get worn down, which can cause a leak. By covering the threads with the plumber’s tape, you may be able to stop the leak. 

Again, turn the water off and completely remove the water supply line. Dry the threads of the fittings with a cloth and then apply the plumber’s tape around them taking care to cover them completely. 

Reattach the supply hose, tightening carefully with a pipe wrench, to hopefully, create a watertight seal and stop the leak. Turn the water back on and check for leaks. If the leak is still there, it might be time to call in a licensed plumber as you have something more serious going on.

FAQs Toilet Leaking From Water Supply Line

Most toilet water supply line leaks are easy to diagnose and fix, but here are a few commonly asked questions and answers that may further help you resolve your issue.

Are toilet water supply lines universal?

No, toilet water supply lines are not universal. They come in a variety of sizes and styles depending on the manufacturer of your toilet. When purchasing a new water supply line for your toilet, take the old part along to the hardware store to make sure you get the right replacement part. 

How do I know the size of my toilet supply line?

Most toilet water supply lines have their size printed on the side of the hose. If you can’t find the size printed on the side of your water supply hose, use a ruler, tape measure, or caliper to measure the diameter of the hose. This should give you a good estimate of the size you need.

How often should you replace the toilet water supply line?

Experts recommend replacing a toilet water supply line every three to five years. Doing so can prevent corrosion and deterioration that can lead to leaks in the water supply. 

Plumber and HVAC Technician | Website | + posts

As a retired Master Plumber Jamie has over 30 years of hands-on experience, making his plumbing knowledge second to none. He has also worked on both residential and commercial HVAC installation and repair projects.