Find and Repair Hidden Plumbing Leaks

Tub and shower: Splash leaks

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Test a shower door

Splash water all around a shower door. If water seeps out from behind the frame, caulk the frame on the inside. Run a new bead along the floor/tub joint.

Splash leaks are simply water escaping past a shower curtain or a shower door. Plumbers tell us it's the most common type of bathroom leak. Although it may sound minor, this leak causes major damage when water seeps into the subfloor where flooring meets the tub or shower. Before long the vinyl flooring or tiles begin to loosen. Even worse, the plywood subfloor delaminates and rots, requiring a huge, expensive tearout and replacement project.

Signs of trouble:

• Curling vinyl flooring or loose tiles next to the tub.
• Peeling paint or flaking, chalky-looking wood finish near the shower.
• Water stains on the ceiling or joists below.
• Mold spots on the wall or floor near the tub or shower.
• If you use a curtain, look for standing water on the floor after you shower.

• If you have a shower door, splash water all around the door and frame. Leaks around the frame may take five minutes or longer to show up.
• If the door has rubber gaskets or a rubber door sweep, check them for gaps.
• Also check for any gaps in the caulk where the shower or tub meets the flooring.

How to fix it:

• Be sure to overlap sliding doors correctly when you close them. The inner door should be closest to the faucet.
• If you have a shower curtain rather than a door, make sure you close it completely when you shower, or add a splash guard.
• Seal a leaking frame by running a small bead of caulk around the inside of the frame. Force the caulk into any gaps between the frame and the shower surround. Quickly wipe away all the excess caulk. When the caulk dries, test for leaks again.
• Replace any worn gaskets or door sweeps. Bring the old one to a home center or plumbing supply store and look for a matching replacement.
• If the old caulk along the floor shows gaps, scrape it out and run a new bead.

Homeowner story:
“I noticed the floor tile along the tub was coming loose. I pushed on it and it crunched down into the underlayment, which was totally rotten. We ended up replacing all of the tile and part of the subfloor.”

Figure A: Common tub and shower leaks

Vulnerable tub corner

Figure A: Tub and Shower Leaks

The most damaging tub and shower leaks occur when water splashes out of the enclosure. Tile and drain leaks can also cause major damage.

Tub and shower: Drain leaks

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Photo 1: Test a drain

Plug the drain with a test plug and add water. After an hour, check to see if the water level has dropped.

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Photo 1A: Close-up of test plug

Measure the drain diameter and buy a test plug to fit.

Drain leaks allow water to sneak around the outside of the drain where it's connected to the tub or shower. This is especially common with plastic or fiberglass tubs and shower pans, since these materials flex slightly when you stand on them, often breaking the seal around the drain. These leaks can stain or destroy the ceiling below or rot floor joists. In the case of a tub set on a concrete slab, the leak will ruin flooring in the bathroom or adjoining rooms.

Signs of trouble:

• Water stains on the ceiling or joists below.
• Loose flooring near the tub or damp floors in adjoining rooms (if the tub is on a concrete slab).

How to find the source:

• If you can see the underside of the drain through an access panel or open ceiling, partially fill the tub and then release the water. In a shower, plug the drain with a rag and then release the water. Check the drains and traps for leaks from below through the access panel.
• If you don't have access to the underside of the drain, plug the drain and add enough water to form a small puddle around the drain (photo). Mark the edge of the puddle by setting a bottle of shampoo next to it. Then wait an hour. If the puddle shrinks, the drain is leaking. Don't rely on your tub stopper for this test; it may leak. Remove the stopper and insert a 1-1/2-in. test plug (find them at home centers). Remove the grate and use a 2-in. plug for a shower.

How to fix it:

• To repair a tub drain, unscrew the drain flange from above. Then clean the flange and apply silicone caulk. Also remove the rubber gasket that's under the tub's drain hole and take it to a home center to find a matching gasket. Slip the new gasket into place and screw in the drain flange.
• If you have access to a shower drain from below, tighten the ring nut that locks the drain to the shower pan. If that doesn't work, replace the drain assembly. If you don't have access beneath the drain, cut a hole in the ceiling below or replace the drain assembly with a WingTite drain.

Tub and shower: Tile leaks

Tile leaks occur when water seeps through deteriorating grout or caulk and gets into the wall behind the tile (Figure A). Depending on the materials used to set the tile, this can lead to tile falling off the wall, severe rotting of the wall framing, and damage to the subfloor, joists or ceiling below.

Signs of trouble:

• Loose tiles.
• Persistent mold.
• If the shower is against an exterior wall, you may find an area of peeling paint outside.
• Stains on the ceiling under the shower.

How to find the source:

• Examine the grout and caulk joints for gaps. You almost always find mold here.
• If you have loose tile behind the tub spout or faucet, open the access panel behind the faucet and look for dampness or stains.

How to fix it:

• Remove the old grout, caulk and loose tiles.
• If the surface behind the tile is still solid, you can reattach tiles, regrout and recaulk.
• If more than a few tiles are loose or if the wall is spongy, you'll have to install new backer board and tile, or a fiberglass surround.

Toilet flange leaks

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Photo 1: Locate the source

Take measurements from stacked walls to find the source of a ceiling stain. In most cases, the stain occurs close to the source.

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Photo 2: Check for flange leaks

Unscrew the toilet bolt nuts and remove the toilet. Scrape away the wax and look for leaks. Also check for cracks around the toilet's horn.

These leaks occur where the toilet meets the waste pipe below. They allow water to seep out at every flush, which will wreck flooring, rot the subfloor and joists, and damage the ceiling below (Photo 1).

Signs of trouble:

• Water seeping out around the base of the toilet.
• Loose or damaged flooring.
• Stains on the ceiling below.
• A toilet that rocks slightly when you push against it. This movement will eventually break the wax seal between the toilet and the closet flange.

How to find the source:
If you have ceiling stains, measure from stacked walls (right photo) before you go through the hassle of removing the toilet. If the stain is near the toilet, a leaking flange is the most likely source. Remove the toilet (Photo 2) and look for these leak sources:

• The flange is level with or below the surrounding floor surface.
• Cracks in the flange.
• Bolts or the slots they fit into are broken.
• The flange is loose, not screwed solidly to the subfloor.

How to fix it:

• If you don't find any of the problems listed above, reinstall the toilet with a new wax ring.
• If the flange is too low, install a plastic flange riser over the existing flange.
• If the flange or bolt slots are broken, install a metal repair flange.
• If the toilet rocks because the floor is uneven, slip toilet shims under the toilet when you reinstall it.

Homeowner story:
“I had noticed the toilet rocking slightly for a few years, but I kept putting off the repair. Then one day the ceiling under the toilet fell in. It turned out that the wax ring had been leaking for years. The subfloor around the toilet was rotted, and the more it rotted, the more the toilet rocked and the more water leaked out with every flush.”

Figure B: Toilet flange leaks

Figure B: Toilet Leaks

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

Sinks: Sink rim leaks

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Test for rim leaks

Dribble water around the sink rim and faucet base with a sponge. Then look for leaks below using a flashlight.

Sink rim leaks allow water to seep under the rim or the base of the faucet. They will gradually destroy your cabinets and countertops in kitchens and bathrooms.

Signs of trouble:

• Puddles, dampness or water stains inside the cabinet.
• Loose plastic laminate near sink.
• A loose faucet base.
• Deteriorating caulk around sink.

How to find the source:

• If you have a plastic laminate countertop, examine the underside of the countertop using a flashlight. Look for swollen particleboard or other signs of water damage.
• Dribble water around the sink rim and look for leaks (photo).

How to fix it:

• Tighten the faucet base by turning the mounting nuts underneath it.
• If the sink rim is caulked, scrape away the old caulk and recaulk.
• Tighten the clips under the sink rim that clamp the sink to the countertop.

Homeowner story:
“The caulk around my cast iron sink was in bad shape for years, but I didn't worry about it until the plastic laminate in front of the sink began to loosen. I stuck my head under the sink and saw that the particleboard under the sink rim was black and swollen. When I poked at the rotten particleboard, it crumbled like charred wood. I had to replace all my countertops at a cost of $800. But I'm glad the old countertop gave me a warning sign—with a few more months of rot, that 100-lb. sink could have fallen into the cabinet below.”

Figure C: Sink leaks

Figure C: Sink Leaks

Sink leaks can occur at any plumbing joint. But the most common leaks happen at the sink rim, shutoff valves, supply line connections and slip joints in the waste lines.

Sink: Supply leaks

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Check for supply leaks

Don't rely on your sense of touch to find tiny leaks. Wipe each connection with a dry tissue. Then look for a wet spot on the tissue.

Supply leaks under the kitchen sink or bath vanity can go unnoticed for a long time since they're usually at the back of the cabinet. Water can run down the pipes into the floor or subfloor, rotting the sink base, the floor and the framing.

Signs of trouble:

• Puddles, dampness or water stains inside the cabinet.
• Stains on the ceiling below.

How to find the source:

• Dab shutoffs and connections with a dry tissue or paper towel and look for wet spots (photo).
• Run the dishwasher and check for leaks under it.

How to fix it:

• If the valve stem on a shutoff valve drips, tighten the packing nut. If the leak doesn't stop, replace the valve.
• For other leaks at the shutoff valve or at the faucet, try tightening the compression nut first. If that doesn't stop the leak, disassemble the fitting, coat the ferrule or gasket with Teflon joint compound (available at home centers and hardware stores) and reassemble the connection.

Sinks: Drain leaks

Drain leaks in kitchens and bathrooms usually occur at the drain or at the slip joints in the drainpipe. Hidden behind boxes and bottles, these leaks can damage flooring, cabinets and even ceilings below before you notice them.

Signs of trouble:

• Puddles, water stains or a dank odor in the cabinet.
• Loose or damaged flooring in front of the sink.

How to find the source:

• Fill the sink bowls, then as they drain check all joints from the sink to the wall with a dry tissue (see photo above).
• Run and drain the dishwasher and check the waste hose connection.

How to fix it:

• For a slip joint leak, first tighten the slip nut. If that doesn't work, disassemble the joint, coat the washer with Teflon joint compound and reassemble.
• For a leak from the basket strainer, tighten the ring nut under the sink. If the leak continues, disconnect and remove the basket strainer. Reassemble it using plumber's putty as a sealant under the basket's rim.

Water meter check

Test for Hidden Leaks

The vast majority of leaks occur at or near plumbing fixtures like tubs, sinks and toilets. But if you suspect a leak in the water supply system, there's a simple way to check it— even if the pipes are hidden inside walls. First, turn off all your faucets. If you have drippy faucets or a toilet that runs between flushes, close the shutoff valves. Then go to your water meter and check the position of the “1-cubic-foot” dial. Check the dial again two hours later. If the dial has moved, you have a leak in the water supply.