old bath tub with pink tile and old faucet

Kendall "aka Renos"

Founder, Lead Instructor of Renos 4 Pros and Joes and Bathroom Update Guide

Bathtub Leak Locations

I’m standing in the unfinished basement of a ranch style home on a service call. The client was cleaning up in her basement earlier in the week and noticed water a small amount of water on the floor. She could see that the water was coming from a bathroom above. It appeared that the water was leaking from somewhere around the bathtub. As I begin to gather information and investigate further into the problem, the homeowner asked, “Where do bathtubs leak?”


Bathroom leaks can come from a few different places. The leak can come from the tub drain where the rough plumbing drain is connected to the bathtub. The tub can also leak at the tub overflow which is also connected to the rough plumbing drain. Tubs can leak around the tub/shower control valve.  Leaks are also common at the front of the tub where it meets the finished floor. In some instances, leaks can also develop around the lip of the tub where it meets the wall tile or tub surround. That was a quick rundown of potential tub leak locations. Let’s discuss each potential problem area and what you can do to address the problem.


What is a Tub Drain?

A tub location is usually found at the lowest point in the bottom of the tub. It is a hole that is designed to allow the water in the tub to drain quickly.


How to detect a tub leak?

Detecting a tub leak CAN be done alone. However, it is so much easier to do with the assistance of another person. You may have to do some trial and error to track down the problem. And this is going to involve repeatedly turning the water on and checking for leaks. Since it’s hard to be in two places at once, a second set of hands and eyes is recommended.


Leak at Tub Drain

Perhaps the most obvious location to expect to find a leak would be at the tub drain. It is the lowest point on the tub, which means that when its open the water will always flow in that direction to escape. It’s also a common location for a leak because you have a connection between different building materials.  

What is a Tub Drain made of?

Most tubs are made from acrylic, fiberglass, steel, cast iron and the drain on the actual tub is made from the same material. Now the rough plumbing portion of the tub can be made from several different materials. The visible portion of the drain is usually made from some type of metal.

But the portion of the rough plumbing that is not visible may be made from PVC (plastic) or brass. In older homes the portion of the tub drain that sits directly under the tub is brass.

If you develop a leak at the floor drain. The first thing you should do is make sure that the metal drain is not snug. If you determine that this is not the problem, you may need to adjust the way that the drain is screwed into the rough plumbing drain below the floor. Before you take this step, be sure to check the rough plumbing drain to make sure that it’s not leaking at a connection below the tub.


Leak at Tub Overflow

On most tubs, the overflow is located directly above the tub floor drain. It’s designed to give you a little extra time to get back to the bathroom and turn the tub water off before it overflows. It is not designed to completely prevent your tub from overflowing. The overflow drain is actually attached to the tub with the same rough plumbing drain as the floor drain even though you can see it unless you look underneath the tub.

The overflow usually is held in place by a bolt or screw and on the back side of the tub there is a ring (usually made of rubber in modern times) that presses against the backside of the overflow drain and when the bolt is tightened on the front side, it creates a watertight seal. If you discover that you have a leak here, start by checking to make sure the bolt is tight.

You also want to make sure that there are no gaps in the cover that the bolt goes through. If there are, you can use silicone to seal around the open areas. Do not silicone the actual overflow part. If you still have a problem, you may have to adjust the drain connection to the tub fix. This may require you access the drain from the underside of the tub.


Leak at Tub/Shower Control Valve

The control valve is a potential leak location that most people don’t think about. The control valve or mixing valve is what allows you to turn the water on and off and adjust hot and cold in the tub. The parts that you can see and touch are referred to as the trim and these parts are usually made of metal but in some cases are made of plastic.

The actual working parts of the controls are installed in the wall and are not visible. These hidden components are actually the parts that are doing all the real work. These parts are usually made of a combination of brass, with rubber and plastic fittings. The trim pieces are actually what blocks water from spraying or running back inside of the wall.

The trim pieces are usually just screwed into place. If you were to remove these trim pieces you would see that there is a hole in the wall where each control comes through the wall. If you discover that you have a leak here, you can usually solve the problem simply by running a bead of silicone sealant around the base of the trim pieces where they meet the shower wall. This will work for tile or fiberglass walls.  


Leak in front of the Tub

Another common location for water leaks is at the front of the tub. This is most common if you have a tub that sits in an alcove and is surrounded on three sides by walls. The area in front of the tub is where the tub intersects with a different building material. Regardless of whether your floors are tile, vinyl, or wood, or some other material, they cannot be physically attached to the tub.

Usually, the flooring material butts up to the edge of the tub. This seam where the tub and floor meet is a weak point where moisture can escape. This issue is magnified by the fact that we have to get in and out of the tub, and usually, when we do, we are soaking wet.

We then transfer water from the tub onto the floor in the same area where we have a weak point. Kids can further contribute to the issue because often they like to splish splash in the tub and get water everywhere including on the floor. And if your tub also has a shower head, then you also have the potential to get water on the floor from the shower. If your shower curtain is too low and water splashes over it, or your shower curtain is not pulled tight to the wall, then water can also find its way to the floor this way.

If you have tile on the floor, the seam where tile and tub meet may be filled with tile grout, it also could be filled with some type of sealant. If your floors are vinyl or most other products this seam is also filled with sealant. If you discover that you have a leak here, you can check the condition of the existing sealant or grout.

If it’s in poor condition you can remove it by scraping or trimming it out with with a razor knife or 5-in-1 tool, and then reapplying sealant. The most commonly used sealant is silicone. Even if you have tile, silicone will likely provide a better barrier than regular grout. You can try grout caulk instead of sealant. The advantage to the grout caulk is that it’s usually available in the same colors as the regular grout, so you can make it all match.


Leak at Tub Surround

The area around the perimeter of the tub where it meets the walls is another potential moisture problem area. A tub that is designed to be installed with a three wall around it usually has a lip that isn’t visible. This lip goes behind the walls. The walls are then attached in front of the lip in order to add moisture protection.

However, if for some reason the tub walls aren’t installed in front of the lip of the tub, this can eventually create an opportunity or moisture to enter the wall. This problem usually doesn’t happen overnight. There should be a small between the bottom of the last tile, and the tub. This gap is frequently filled with grout during tile installation.

It’s common and normal for the grout in this gap to crack over time. Grout caulk is a better product to use where these building materials meet. The caulk is flexible and can stand up to more movement from the tub and the home. You can simply remove the old grout using the methods mentioned above and then apply caulk to the gap. If you have a fiberglass surround that is leaking you can use silicone instead of grout caulk.

Be aware that if moisture gets into the wall it can lead to a whole host of other problems besides water on the floor in the space below; including causing the tiles to come loose.