How To Find And Repair Hidden Plumbing Leaks

Locate and repair concealed plumbing leaks

Locate and repair tiny leaks before they cause serious harm.

We demonstrate basic methods for locating and repairing common water leaks before they cause rot and other costly damage. The majority of them are found near bathtubs and showers, as well as drains, sinks, and toilets.

Splash water all over the shower door. Caulk the interior of the frame if water leaks out from beneath it. Make a new bead of glue and run it along the floor/tub joint.

Splash leaks are just water escaping through a shower curtain or door. According to plumbers, this is the most common form of bathroom leak. Although it may appear to be a little leak, it causes significant damage when water seeps into the subfloor where the flooring meets the tub or shower. The vinyl flooring or tiles will begin to loosen after a short period of time. Worse, the plywood subfloor delaminates and rots, necessitating a massive, costly tearout and replacement effort.

Symptoms of trouble:

Curving vinyl flooring or loose tiles near the tub
Near the shower, there is peeling paint or a flaking, chalky-looking wood finish.
Water stains on the ceiling or the joists beneath.
Spots of mould on the wall or floor near the bathtub or shower.
After showering, watch for standing water on the floor if you use a curtain.
How to locate the source of a leaky bathtub drain:
Splash water all around the shower door and frame if you have one. Leaks around the frame may take up to five minutes to appear.
Check for gaps in rubber gaskets or a rubber door sweep if the door has them.
Also, look for any caulk gaps where the shower or tub meets the flooring.

How to Repair a Leaking Bathtub Drain:

When closing sliding doors, make sure you overlap them correctly. The inner door should be nearest the faucet.
If you have a shower curtain instead of a door, make sure it is completely closed when you shower, or instal a splash guard.
Run a tiny bead of tub and caulk along the inside of a leaking frame to seal it. Fill any gaps between the frame and the shower surround with caulk. Wipe away any excess caulk as soon as possible. When the caulk has dried, check for leaks once more.
Any worn gaskets or door sweeps should be replaced. Bring the old one to a home centre or plumbing supply store and look for a replacement that is a match (be sure to get the correct size to fit).
Scrape out the old caulk along the floor and replace it with a new bead.
The following is a homeowner’s storey:
“I noticed the floor tile along the tub was loosening. When I pushed on it, it crunched down into the rotting underlayment. We ended up having to replace all of the tile as well as a portion of the subfloor.”

Leaks in the Tub and Shower

When water splashes out of the enclosure, the most severe tub and shower leaks occur. Leaks in tiles and drains can potentially cause significant damage.

Figure A: Leaks in the tub/shower.
Figure A shows a close-up of a tub corner.
Drain leaks in the tub and shower

Photo 1: Run a drain test
Plug the drain with a test plug and fill it with water. Check to see if the water level has dropped after an hour.

Drain leaks allow water to enter the drain where it is connected to the tub or shower. This is especially common with plastic or fibreglass tubs and shower pans since they bend somewhat when you stand on them, frequently breaking the seal around the drain. These leaks have the potential to discolour or ruin the ceiling below, as well as rot the floor joists. If the tub is set on a concrete slab, the leak will destroy the flooring in the bathroom or nearby rooms.

Bathtub drain leaking warning signs:
Water stains on the ceiling or the joists beneath.
Loose flooring near the tub or wet floors in adjacent rooms (if the tub is on a concrete slab).
To locate the source of a leaky tub drain, follow these steps:
If you can see the underside of the drain through an access panel or an open ceiling, fill the tub halfway and then let it drain. When taking a shower, seal the drain with a rag and then turn off the water. Through the access panel, inspect the drains and traps for leakage.
If you don’t have access to the drain’s underside, plug it and fill it with enough water to produce a small puddle around it (photo). Set a bottle of shampoo next to the puddle to mark its edge. Then, after an hour, repeat the process. The drain is leaking if the puddle shrinks. For this test, do not rely on your tub stopper; it may leak. Remove the stopper and replace it with a 1-1/2-in. test plug (find them at home centers). Remove the grate and instal a 2-inch shower plug.
How to Repair a Leaking Bathtub Drain: To repair a tub drain, detach the drain flange from above. The flange should then be cleaned and silicone caulk applied. Remove the rubber gasket from beneath the tub’s drain hole and take it to a home improvement store to be replaced with a matching gasket (be sure to get the correct size to fit). Insert the replacement gasket and screw in the drain flange.
Tighten the ring nut that secures the shower drain to the shower pan if you have access to it from below. Replace the drain assembly if that doesn’t work. If you can’t get beneath the drain, cut a hole in the ceiling or replace the drain assembly with a WingTite drain.
Bathtub and shower: Leaking tiles
Water seeps through disintegrating grout or caulk and into the wall behind the tile to cause a leak (Figure A). This can result in tile falling off the wall, serious rotting of the wall frame, and damage to the subfloor, joists, or ceiling below, depending on the materials used to set the tile.

Symptoms of trouble:

Tiles that are loose.
Mold that is persistent.
If the shower is facing an exterior wall, there may be some peeling paint outside.
Under the shower, there are stains on the ceiling.
How to locate the source:

Check for gaps in the grout and caulk joints. Mold is almost usually present here.
Open the access panel behind the faucet and inspect for wetness or stains if you have loose tile behind the tub spout or faucet.

How to repair it:

Get rid of the old grout, caulk, and loose tiles.
If the surface behind the tile is still firm, reattach the tiles, regrout, and recaulk with tub and tile caulk.
If more than a few tiles are loose or the wall is squishy, you’ll need to replace the backer board and tile, or build a fibreglass surround.
Leaking toilet flanges

Photo 1: Find the source
To locate the source of a ceiling stain, take measurements from stacked walls. In most situations, the stain appears near the source.

These leaks happen where the toilet connects to the waste pipe below. They enable water to seep out with each flush, destroying flooring, rotting the subfloor and joists, and damaging the ceiling below (Photo 1).

Symptoms of trouble:

Water oozing out of the toilet’s base.
Flooring that is loose or damaged.
Below are stains on the ceiling.
When you press against it, the toilet rocks somewhat. This movement will finally dislodge the wax seal that has formed between the toilet and the closet flange.
How to locate the source:
If you have ceiling stains, take measurements from stacked walls (right photo) before removing the toilet. If the stain is near the toilet, the most likely cause is a leaking flange. Remove the toilet (Photo 2) and search for the following leak sources:

The flange is at or below the level of the surrounding floor surface.
The flange has cracks.
Bolts or the slots into which they fit are broken.
The flange is loose and not securely fastened to the flooring.
How to repair it:

If none of the problems described above are found, refit the toilet with a new wax ring.
Install a plastic flange riser over the existing flange if the flange is too low.
Install a metal repair flange if the flange or bolt slots are broken.
If the toilet rocks because the floor is uneven, place toilet shims beneath it when reinstalling it.
“I had noticed the toilet swaying slightly for a few years, but I kept putting off the repair,” says the homeowner. Then one day, the ceiling beneath the toilet caved down. The wax ring had been seeping for years, it turned out. The subfloor around the toilet was rotten, and as it deteriorated, the toilet rocked and more water leaked out with each flush.”

Toilet Leaks

Toilet leaks can occur from the water supply or the tank, but the most serious leaks occur at the flange and wax ring.

Figure B: the toilet.
Sinks: Leaking sink rims

Check for rim leaks.
Using a sponge, dribble water along the sink rim and faucet base. Then, using a flashlight, search for leaks below.

Sink rim leaks allow water to seep under the rim or into the faucet’s base. They will progressively deteriorate your kitchen and bathroom cupboards and counters.

Symptoms of trouble:

Inside the cabinet, there are puddles, wetness, or water stains.
Near the sink, there is a piece of loose plastic laminate.
A faulty faucet base.
Caulk around the sink is deteriorating.
How to locate the source:

If you have a plastic laminate countertop, use a flashlight to inspect the underside of the countertop. Examine the particleboard for swelling areas or other evidence of water damage.
Look for leaks by dribbling water around the sink’s rim (photo).

How to repair it:

Turn the mounting bolts underneath the faucet base to tighten it.
Scrape away the old caulk and recaulk the sink rim if it is caulked.
Tighten the clamps that hold the sink to the countertop beneath the sink rim.
“The caulk surrounding my cast iron sink had been deteriorating for years, but I didn’t notice it until the plastic laminate in front of the sink began to loosen.” When I poked my head under the sink, I noticed that the particleboard behind the sink rim was dark and bloated. When I prodded the rotten particleboard with my finger, it disintegrated like burnt wood. I had to replace all of my countertops, which cost $800. But I’m grateful the old countertop gave me a heads-up—with a few more months of deterioration, that 100-pound sink could have collapsed into the cupboard below.”

Sink Leaks are seen in Figure C.
Sink leaks can occur at any point in the plumbing system. However, the most typical leaks occur at the sink rim, shutoff valves, supply line connections, and waste line slide joints.

Figure C: Sink Under Sink Plumping: Leaks in the Supply

Look for any supply leaks.

You should not rely on your sense of touch to detect little under-sink plumbing leaks. Using a dry tissue, wipe each connection. Then search the tissue for a damp area.

Supply leaks under the kitchen sink or bathroom vanity might go undetected for a long time since they are normally located at the back of the cabinet. Water can leak from the pipes into the floor or subfloor, ruining the sink base, floor, and framework.

Symptoms of under-sink plumbing problems include:

Puddles, wetness, or water stains beneath the sink and within the cabinet.
Below are stains on the ceiling.
How to locate the source:

Examine shutoffs and connections for moist spots with a dry tissue or paper towel (photo).
Run the dishwasher and look for leaks beneath it.

How to repair it:

Tighten the packing nut on a shutoff valve if the valve stem drips. Replace the valve if the leak does not stop.
Tighten the compression nut first for other leaks at the shutoff valve or faucet. If this doesn’t work, dismantle the fitting, treat the ferrule or gasket with Teflon joint compound (available at home centres and hardware stores), and reconnect the connection.
Sinks: Leaks in the drain
Drain leaks in kitchens and bathrooms are most commonly found at the drain or at the slip joints in the drainpipe. These leaks, which are hidden behind boxes and bottles, can cause damage to the floors, cabinets, and even the ceilings below before you realise them.

Symptoms of trouble:

In the cabinet, there may be puddles, water marks, or a musty stench.
In front of the sink, there is sagging or ruined flooring.
How to locate the source:

Fill the sink bowls, then as they drain, use a dry tissue to inspect any joints from the sink to the wall (see photo above).
Check the waste hose connection then run and drain the dishwasher.

How to repair it:

Tighten the slip nut first to fix a slip joint leak. If that fails, dismantle the joint, treat the washer with Teflon joint compound, and reassemble.
Tighten the ring nut under the sink to stop a leak from the basket strainer. If the leak persists, unplug and remove the basket strainer. Reassemble it with plumber’s putty as a sealer beneath the basket’s rim.
Two Slow Leaks Predicting a Catastrophe

Check the pressure relief valve and the drain valve if you detect puddles near your water heater. Replace the valve if either is dripping. If not, the tank is leaking and you will need to replace the water heater. Don’t put it off. Tank leaks frequently begin slowly and then burst abruptly days or weeks later, causing a massive household flood. The same can be said of washing machine supply hoses. Replace the hose if you discover a tiny leak in it or at the crimped metal fittings at the ends. Otherwise, the hose will eventually rupture, producing a steady stream of water.

Examine for Unnoticed Leaks

The great majority of leaks occur near or on plumbing fixtures such as tubs, sinks, and toilets. However, if you suspect a leak in the water supply system, there is an easy way to check it—even if the pipes are buried behind walls. To begin, turn off all of your faucets. Close the shutdown valves if you have dripping faucets or a toilet that runs between flushes. Then, go to your water metre and look at the “1-cubic-foot” dial. Check the dial again in two hours. If the dial has shifted, there is a leak in the water supply.


This Project’s Required Tools

Have all of the tools you’ll need for this DIY project ready before you begin to save time and stress.

Screwdriver with four blades
Wrench with adjustability
Caulking gun
Flashlight
Plier with a slip joint
Knife for general use
Required Items for this Project Prepare all of your materials ahead of time to avoid last-minute shopping expeditions. Here’s a list of them.

Drain plug caulk
Seals and gaskets
Toilet shims Silicone caulk Wax ring