What’s That Smell? Common Summer Plumbing Odors And How To Fix Them

There’s nothing like opening your windows on a summer day—until an unpleasant smell starts wafting through your home. If you’ve noticed strange plumbing odors during the warmer months, you’re not alone. Summer heat and humidity can intensify hidden plumbing issues, making certain smells more noticeable—and more frustrating.

At Niebuhr Plumbing, Heating, and Air Conditioning, we often hear from La Crosse homeowners dealing with sour, musty, or sewer-like odors that seem to come from nowhere. The good news? These smells are often caused by common plumbing issues that can be addressed with a few simple fixes or preventative steps.

Let’s break down the most common causes of summer plumbing odors, what they might mean, and how you can fix (or prevent) them.

1. Sewer Gas Smell

What it smells like: Rotten eggs or sulfur
Where it’s coming from: Drains, bathrooms, laundry rooms, or basements

What’s going on:

A sewer gas smell is typically caused by a dry or blocked P-trap. P-traps are the curved sections of pipe under sinks and floor drains that hold water to prevent sewer gases from entering your home. If the water in a trap evaporates—especially in unused fixtures—there’s nothing to block that smell from rising back up.

It could also indicate:

• A cracked or broken vent pipe, which allows sewer gas to escape inside the home instead of venting outdoors
• A more serious issue in your sewer line, especially if multiple drains are affected

How to fix it:

• Run water down infrequently used sinks, showers, or floor drains to refill the P-trap.
• Pour a small amount of mineral oil into the drain to slow evaporation in fixtures that are rarely used.
• If the smell persists or spreads, it’s time to call a licensed plumber to check for a venting or sewer line issue.

2. Musty Or Moldy Smell

What it smells like: Damp basement or mildew

Where it’s coming from: Under sinks, in cabinets, around fixtures

What’s going on:

Warm summer air combined with minor plumbing leaks can lead to mold and mildew growth in hidden places. Even a slow drip from a pipe joint or faucet can create the perfect conditions for mold spores to thrive—especially in dark, enclosed spaces.

How to fix it:

• Inspect under sinks and behind toilets for signs of moisture, warped wood, or discoloration.
• Tighten any loose fittings and replace worn washers or seals.
• Use a mold-killing cleaner and dry the area thoroughly. In persistent cases, you may need to replace cabinetry or drywall.

3. Foul Odors From The Kitchen Sink

What it smells like: Sour or rotting food
Where it’s coming from: Kitchen drain or garbage disposal

What’s going on:

In summer, food particles break down faster in the heat and can get trapped in your garbage disposal or drain, causing bacteria to grow and smells to develop.

How to fix it:

• Run cold water for 30 seconds before and after using the disposal.
• Drop in ice cubes and a few lemon peels, then turn the disposal on to clean and deodorize the blades.
• Avoid pouring grease or oil down the drain—they can harden and trap food debris.

4. Sulfur Smell In Water

What it smells like: Rotten eggs, but only when using water
Where it’s coming from: Hot water taps or all fixtures

What’s going on:

If the smell is only present when using hot water, the issue is likely your water heater. Bacteria in the tank can interact with the anode rod, producing a sulfur-like smell.

If the smell occurs with both hot and cold water, it could be due to naturally occurring sulfur or iron bacteria in your well or municipal supply.

How to fix it:

• Have your water heater flushed and disinfected.
• Consider replacing the anode rod with one designed to reduce odors.
• If your home uses well water, you may benefit from a whole-home filtration or softening system.

5. Stinky Floor Drains

What it smells like: Sewage or mildew
Where it’s coming from: Floor drains in basements, laundry rooms, or utility areas

What’s going on:

Infrequently used floor drains can suffer from dry traps, similar to sink drains. If your basement is humid, stagnant water in the trap or nearby sump pump pit can develop mold, mildew, or bacterial odors.

How to fix it:

• Pour water down the drain monthly to keep the trap filled.
• Add a splash of vinegar to help eliminate bacteria.
• Check that your sump pump is functioning properly and draining water as expected.

Final Thoughts

Summer is a time to enjoy fresh air—not fight off unpleasant plumbing smells. Whether it’s sewer gas creeping in through dry drains or organic buildup in your garbage disposal, the key is understanding plumbing odors and what’s causing them to address it early.

If the smell persists—or you’re not sure where it’s coming from—it’s a good idea to bring in a licensed professional. At Niebuhr Plumbing, Heating, and Air Conditioning, we’ve been helping La Crosse homeowners tackle plumbing issues big and small for over 120 years.