The 7 warning signs your home has mold in the plumbing, what to never ignore and why you must act now

Mold in the home is a problem, both for your health and the gnarly aesthetics. However, some mold can be hidden and you won't realize it's there unless you're specifically looking out for it.

Here, our plumbing experts reveal the X signs there is mold in your plumbing, why it happens, and how to fix it.

Whilst some of the reasons cannot be avoided, having the habits that increase the risk of mold in your home on your radar will definitely help.

The signs of mold in plumbing

Unlike mold creeping up a wall and in clear sight, the signs of mold lurking in plumbing can be more subtle.

Rinea Blanchard founder and CEO of Superior Contract Cleaning has more than 25 years experience in home restoration and cleaning and removed mold from plumbing many times. She says, 'Even though it's far more common in drywall, attics, and insulation, it can also happen in plumbing.'

Aside from unexplained or exacerbated respiratory issues, here are the signs Blanchard says to watch out for:

• Visible mold around sinks, faucets and drains.
• If you notice a persistent musty,earthy smell, especially after showering, that's a red flag. In one client's home, Blanchard traced a stubborn mildew scent to mold growing in their shower drain.
• Dark or discolored water coming from your faucets can indicate mold in the pipes. If there's black sludge, that's a telltale sign of mold buildup.
• Mold can accumulate in drains, causing clogs. Blanchard often finds this in bathroom sinks and showers where there's lots of organic material for mold to feed on. If there is a slow draining sink or blocked tub, you may want to take a deeper look with mold in mind.
• And last but not least, a sneaky sign could be persistent grout mold. If you're constantly cleaning tile grout or bathtub caulking to remove mold, the source might actually be in your pipes.
• HVAC pro, Allen Chenault of AC's Heating and Air adds, 'The smell of mustiness near water heaters or in the basement is usually one of the first signs of mold in plumbing. This means excess moisture has led to mold spores forming colonies, releasing spores and VOCs into the air.

Why it happens

Usually, there is an underlying moisture issue and blockages that needs fixing or cleaning which leads to mold in piping. Poor ventilation and leaks are also causes.

Bob Shupe, owner of professional mold removal company, Cleaner Guys with over 25 years experience in mold remediation. He adds, 'If a home has been abandoned for a long time, and the water was not drained out of the plumbing as it should have been, there is a chance that mold could grow inside the plumbing.

'In an unoccupied house, the water is not being turned on and flowing through the plumbing regularly. So water could potentially sit in the pipes long enough that algae could grow, and the algae could then be a food source for mold.'

He adds for mold to occur, it needs moisture, oxygen and an organic food source as well as steady warm temperatures in order to grow. 'The inside of regularly used plumbing has little oxygen, constantly fluctuating temperatures, and little to no organic material, because the high-pressured water flow washes it away. This makes it a pretty inhospitable place for mold growth.

'Additionally, the water supply in the United States is usually treated with disinfectants like chlorine, which further prevents mold from growing inside plumbing.'

If you have leaks and blockages however, this can bring mold.

The risks of having mold in plumbing

Mold releases spores and this can bring respiratory issues and exacerbate existing ones including asthma and COPD, making mold a danger to health.

Rinea Blanchard, of Superior Contract Cleaning says, 'Mold needs to be properly removed and the underlying moisture issue fixed. Not to mention that you'd still keep breathing in the spores which may have a certain hazard called mycotoxins. These have been linked with a plethora of health issues, ranging from less to more severe.'

How to pin point the source

Rinea says to 'check around faucets, shower heads, and pipe connections. Any mold you see on the outside could mean there's more inside the plumbing.'

HVAC pro Allen Chenault finds the source of household leaks by checking anywhere water flows or sits like drains, water heaters and attics. He explains, 'Small spots of black growth are early-stage mold, but if unaddressed can spread into thick mats, as in one case where a leaky attic pipe dripped on insulation for months. By the time the owner called me, massive mold patches coated the attic, requiring hazmat suits to remediate.'

David Ellingsen is a professional plumber and founder of Metropolitan Plumbing. He explains, 'You'll usually find the smell stronger in places with constant moisture, like under sinks, around tubs or showers, or basement utility rooms near water heaters or sump pumps. That's where condensation can build up, especially if the ventilation isn't great. Dark, soggy spots on surfaces are another telltale mold sign I watch out for.

'If a client reports respiratory issues or allergies, that's when I really start probing around with moisture meters and thermal cameras to track down any trouble spots before the mold takes over. Left alone, it can burrow deeper into walls and grow between floor joists. Then you've got a real mess on your hands.'

How to fix it

Josh Mitchell, experienced plumbing technician and owner of Plumbing Lab gives a handy checklist for fixing mold in plumbing:

• Investigate the source: Identify where the smell is strongest
• Confirm moisture presence: Use a moisture meter to detect wet spots.
• Clean affected areas: Apply a mold-killing solution, such as bleach and water, to surface mold.
• Clean the drains: To clean drains, use about ½ cups of baking soda followed by ½ cups of vinegar, available on Amazon. After letting it sit for a few minutes, flush it with 2 cups of boiling water. For stubborn mold in plumbing, you can use mold remover sprays or foaming drain cleaners that expand to clean out the buildup. Enzymatic cleaners (such as Green Goblin Enzyme Drain Cleaner) are also good because they use natural ingredients to break down mold.
• Repair leaks: Address the underlying moisture issue by fixing any leaks.
• Improve ventilation: Ensure proper airflow in high-humidity areas and that the area is well-ventilated during and after treatment.
• Prevent recurrence: After repairs, treat the area with a mold-resistant primer before sealing it back up.

When Ellingsen finds the source of mold in plumbing, his first step is to fix any leaks immediately. He says, 'Even tiny drips provide sustenance for mold. After that, I like to hit it aggressively with a commercial cleaner called Concrobium. It's important to tackle mold early before it can spread.'

Having one of the best dehumidifiers are a must for bathrooms and basements to control future moisture. Ellingsen adds, 'Coordination with HVAC contractors can also rule out any ventilation or air quality issues feeding the mold. Regular plumbing inspections help catch minor problems before they mushroom into bigger drain blockers or pipe cracks.'

The key is not to ignore musty smells and use air fresheners to mask the problem instead of solving it.

Ellingson adds, 'Harsh chemicals without ventilation can also make the problem worse. And never try to salvage water-soaked materials like drywall – it's best to fully replace them. Addressing moisture issues promptly usually does the trick of stopping mold in its tracks.'

Evie Graham, cleaning expert and owner of Waste Direct says, 'When I’ve come across this issue during my work, I’ve found that enzyme-based cleaners work well. They’re safe for your pipes and help break down the buildup without causing damage.'

What not to do

If you're thinking about using bleach, take pause. Allen Chenault says, 'Bleach only kills surface mold, not roots, and damages plumbing. I recommend EPA-registered disinfectants, then flushing pipes to remove contamination. Preventing moisture and promptly repairing any leaks are key.'

Proper and improved ventilation, like running exhaust fans, helps control humidity that feeds mold. Chenault adds, 'One client’s mold problem resolved by fixing their non-vented dryer, which had been dispersing hot, damp air into their attic for years. Small changes can have big impacts.'

Clean surfaces with mold using vinegar. Vinegar is effective and kills mold on surfaces.

Evie Graham warns against using strong chemical drain cleaners. 'Not only can they be harmful to the plumbing but they often mask the problem without really solving it.'

How to prevent it moving forward

Rinea says, 'To spot these mold in plumbing issues on time, do regular inspections and look closely at pipe joints, drain openings, and areas around fixtures. Use a flashlight to peer down drains. If you suspect mold, whatever you do, don't just cover up the problem. I've seen people caulk over moldy areas or use bleach thinking it'll solve everything. That often makes things worse.'

Learn more about caulking and grouting mistakes in our dedicated guide.

For DIY maintenance, she also recommends using enzymatic drain cleaners regularly. 'They're safer than harsh chemicals and help prevent buildup', she says. 'Also, run exhaust fans during and after showers to reduce moisture, which mold needs to survive.'

Next, learn about the common types of household mold and how to get rid of black mold.