If your water smells moldy, it can feel unsettling. You pour a glass and notice an earthy, musty odor, or maybe your hot water smells like mildew whenever you shower. Sometimes, water from faucet tastes moldy, making it unpleasant to drink. The smell itself is usually not harmful, but it signals a problem in your plumbing system, water heater, or even your water source.
This guide explains:
- What causes moldy-smelling water
- What it means for your health
- How to fix and prevent it
Why Your Water Smells Moldy
You might ask, why does my water smell like mildew? The moldy or musty smell in water usually comes from organic compounds created by algae and bacteria. Two major compounds are:
- Geosmin – gives soil its earthy smell after rain
- MIB (2-methylisoborneol) – another compound linked to blue-green algae
Both of these compounds are extremely potent; humans can detect them at parts per trillion levels. In other words, it takes only a tiny amount to make your water smell musty or earthy. While the odor can be unpleasant, it’s important to know that these compounds are not harmful, and your water is generally safe to drink. Still, a persistent smell can signal minor water quality issues in your plumbing or water heater, so it’s worth checking the source and maintaining your home’s water system to keep it fresh.
Common Causes of Moldy Water Smells
Smelly water with a foul odor can be alarming, and identifying the source of the odor is the first step to solving the problem. Here are the most likely reasons it is found in water:
- Municipal water supplies: Algae blooms in lakes or reservoirs used by city water systems can release organic compounds that make tap water smell musty or earthy. Even treated city water may occasionally carry traces of these compounds, producing a subtle but noticeable foul odor.
- Private wells: Water drawn from wells can pick up contaminants from surface runoff, poor sealing, or decaying organic matter. This often results in smelly water that may resemble sewage or moldy odors.
- Plumbing system issues: Stagnant water and biofilm—slimy microbial films that grow inside pipes—are common sources of musty or moldy water. These microbial colonies can produce a persistent foul odor, affecting both cold and hot water.
- Water heater problems: Sediment buildup, chemical reactions to the anode rod, or bacterial growth in water heaters can create smelly water with an unpleasant, sometimes sewage-like, smell. Hot water may be particularly affected.
- Drain and sink sources: Even if the water itself is clean, decaying organic matter or mold in the drain can mimic tap water odor. In some cases, the source of the odor is not the water supply but the sink or drain itself, producing water that smells moldy or foul when first poured.
Example: In Southern California, a 2025 algae bloom in reservoirs led to noticeable earthy odors in city water for weeks, even though tests showed water safety.
Is Moldy-Smelling Water Unsafe?
Most of the time, musty-smelling water is safe to drink. That’s because your nose detects odor long before harmful levels are reached. But odor can still point to deeper water quality problems.
Key Facts
- Detection threshold: People can detect geosmin and MIB in home water or public water at levels far below any health concern. This is why smelling water doesn’t necessarily mean it’s unsafe.
- Municipal water systems: Generally considered safe, since water is disinfected and filtered. However, even in treated tap water, you may notice subtle odors, which is why some people report that their tap water smells moldy occasionally.
- Private wells: Present a higher risk because they often lack regular monitoring and treatment. Homeowners using wells should be alert to any unusual smells in home water, as it could indicate microbial growth or contamination.
When to Worry
Call for help or test your water when you notice unusual odors or signs, because these can indicate more serious water issues. For example:
- The smell lasts more than a few days, or you encounter foul-smelling water that often lingers even after running taps.
- Both the taste and smell are moldy or earthy, suggesting that organic compounds or bacterial growth may be slowly deteriorating into your water.
- You see cloudiness, slime, or unusual coloration, which can indicate sediment, biofilm, or other contaminants affecting water quality.
- Household members experience respiratory irritation, stomach upset, or other health symptoms that may be linked to the water.
- You rely on a private well that hasn’t been tested recently.
Even if the odor seems minor, the smell could indicate bacterial growth, sediment buildup, or other plumbing issues that may affect water quality.
Special concern groups: Children, the elderly, and anyone with weakened immunity should be extra cautious.
Quick Troubleshooting Guide
Follow this step-by-step process to identify the source of the smell.
Check if it’s all taps or one tap only.
- If only one faucet smells → problem in that fixture or drain.
- If all taps smell → could be your water source or heater.
Test hot vs. cold water.
- If only hot water smells moldy → problem likely in water heater.
- If both → may be plumbing or source water.
Smell the glass directly vs. drain.
- Fill a clean glass with cold tap water, step away from the sink.
- If glass smells clean but sink smells bad → odor comes from drain mold or debris.
Check water heater.
- Flush sediment, inspect anode rod, or schedule maintenance.
Look for standing water or dampness.
- Moist areas under sinks or near pipes can grow mold that smells like mildew.
⚠️ Stop using water immediately and test it if:
You should stop using water and have it tested immediately if you notice any of the following warning signs:
- The water smells moldy and has a strong rotten egg smell, which is often caused by hydrogen sulfide or sulfur compounds.
- Water looks discolored, cloudy, or slimy, indicating possible contamination or microbial growth.
These signs suggest that the water may not be safe for drinking, cooking, or bathing, and professional testing is recommended to identify the exact cause.
DIY Fixes for Moldy Water Smell
You can try these fixes at home before calling a professional.
Drain Cleaning
- Add baking soda – Pour half a cup of baking soda into the drain. This helps loosen debris and buildup that can affect your home’s water.
- Add vinegar – Pour a cup of vinegar into the drain. The reaction helps break down mold and grime.
- Let it sit – Wait 15 minutes to allow the mixture to work. This step targets areas where water has a musty smell.
- Flush with boiling water – Rinse thoroughly to clear out loosened debris. This simple routine can help get rid of musty water and improve the taste and odor of your tap water.
Flush Your Water Heater
- Turn off the heater – Always switch off the power or gas supply before performing any maintenance.
- Attach a hose to the drain valve – Connect a hose to the drain or water heater valve to safely direct the water outside or to a floor drain.
- Flush out sediment – Open the valve and let the water run until sediment, minerals, and buildup are cleared. This helps reduce odors and improve water quality.
- Replace the anode rod if needed – For stubborn odors, consider replacing the magnesium anode rod with an aluminum one. If your heater is old or damaged, you may also choose to install a water heater maintenance kit to prevent recurring issues.
Use Carbon Filtration
- Install activated carbon filters – These filters are effective for water treatment and can remove organic compounds that cause an unpleasant smell. If your home’s water has a persistent musty or moldy odor, consider installing RO system (Reverse Osmosis system) as part of your water treatment plan. RO systems use multiple filtration stages—including activated carbon—to remove geosmin, MIB, and other organic compounds.
- Affordable and convenient – Carbon-based water filters are a cost-effective solution for improving taste and odor, making tap water more enjoyable and ensuring it is water safe to drink.
- Regular replacement – To maintain effectiveness, replace filters as recommended by the manufacturer, especially if your water is prone to musty or moldy odors.
Run Water Until Fresh
- If you’ve been away from home – Water that has been sitting in pipes for several days can become stagnant and may develop a musty or moldy smell, especially in rarely used faucets.
- Run taps for a few minutes – Let both hot and cold water flow until it smells and tastes fresh. This simple step helps clear pipes of sediment and microbial buildup, making your home’s water safe and pleasant to use again.
Pros and Cons of DIY Fixes
| Fix | Pros | Cons |
| Drain cleaning | Low-cost, quick | May not solve odor from water source |
| Flushing water heater | Removes buildup | Can be messy/time-consuming |
| Carbon filter | Works well on odor | Needs frequent replacement |
| Flushing taps | Easy, free | Temporary fix only |
Recommendations:
- Start with drain cleaning and flushing taps to quickly improve water quality.
- If odors persist, flush the water heater and consider installing carbon filters for long-term odor control.
- For well water or persistent problems, professional water testing is advised to ensure water is safe to drink and free of harmful bacteria.
Professional & Advanced Solutions
If DIY fixes don’t solve the problem, consider professional treatment or testing.
When to Test Your Water
- You use a private well – Unlike public water supplies, private wells aren’t regularly monitored, so testing ensures your water remains safe. According to the CDC, water testing is recommended for private wells to ensure safety, as odor can still indicate potential contamination.
- Smell lasts longer than 1–2 weeks – Persistent odors that don’t go away after running taps can indicate bacterial growth or other contaminants.
- Water looks cloudy or colored – Changes in appearance, unusual sediment, or off-tastes may signal underlying water quality issues.
- Anyone in the house gets health symptoms – Stomach upset, nausea, or respiratory irritation can be a warning that the water contains harmful microbes or chemicals.
Testing early allows you to identify potential water issues before they worsen. It also gives peace of mind, confirming that your tap water is safe, clean, and pleasant to use every day. Regular monitoring is especially important for private wells and older plumbing systems.
Advanced Solutions for Moldy or Musty Water Smell
| Solution | Best For | Cost | Notes |
| Activated carbon filtration system | Organic odorants (geosmin/MIB) | $$ | Industry standard for odor removal |
| Reverse osmosis | Wells, unknown contaminants | $$$ | Removes wide range of chemicals |
| UV disinfection | Kill bacteria in wells | $$ | Doesn’t remove odor but kills microbes |
| Shock chlorination (well water) | Bacterial contamination in wells | $ | Very effective short-term |
| Professional plumbing service | Biofilm in pipes, heater issues | $$-$$$ | Needed for persistent odor |
Analysis:
- Filtration-focused solutions: Activated carbon and reverse osmosis systems are highly effective at removing organic compounds and other contaminants that cause musty water smell. Carbon water filtration system is cost-effective for ongoing odor control, while RO provides more comprehensive purification for wells or unknown contaminants.
- Bacteria-focused solutions: UV disinfection and shock chlorination target microbial growth in wells. UV systems are preventive, killing bacteria without altering odor, whereas shock chlorination is a short-term treatment for bacterial contamination.
- Professional services: Persistent odors caused by biofilm, plumbing issues, or water heater problems often require professional inspection and treatment.
Recommendations:
- For organic odorants, install an activated carbon filtration system as a standard solution.
- If water comes from a private well or contains unknown contaminants, consider reverse osmosis for comprehensive water treatment.
- For microbial contamination, UV disinfection or shock chlorination is effective.
- Persistent odor issues despite DIY measures should prompt a professional plumbing service to inspect and remediate the system.
Preventing Musty Water Odors Long-Term
Proactive care is key to avoiding water problems and keeping your home’s water fresh and safe. Regular maintenance can help you determine the source of any unpleasant odors before they become serious.
Maintenance Checklist
- Seasonal algae blooms – Install point-of-use carbon filters to reduce musty odors caused by geosmin or MIB in your water supply.
- Flush water heater every 6–12 months – Sediment and bacteria buildup can make water smells moldy or like rotten eggs; regular flushing helps prevent this.
- Run taps weekly in little-used bathrooms – Prevents stagnant water that can develop a musty or moldy smell.
- Check for leaks under sinks – Moist areas encourage mold growth, which can affect water odor.
- Well owners – Perform annual bacteria testing and consult water experts if unusual smells or discoloration appear.
📌 Tip: Print a maintenance calendar to track tasks like flushing, testing, and filter replacement. Staying proactive ensures your water remains clean, safe, and free from musty or foul odors.
Real-World Case Studies
- City Water Event In California’s San Fernando Valley, residents reported that their tap water smells modly during May 2025. Testing confirmed elevated geosmin levels due to algae blooms. The odor lasted weeks but water safety was never compromised.
- Private Well Example A rural family reported their well water smelled musty after heavy rainfall. Testing confirmed bacteria. Shock chlorination and installation of carbon filtration fixed the issue.
- Household Plumbing Example A homeowner noticed shower water smelled like mildew. Inspection showed sediment and bacteria in the water heater, which was fixed by flushing and replacing the anode rod.
Conclusion
If your water smells moldy, don’t panic. Most of the time, it comes from harmless compounds like geosmin or mild plumbing issues. But odors should never be ignored.
- Check the source using step-by-step troubleshooting.
- Try DIY cleaning and filtration first.
- Call a professional or test your water if odors persist.
A moldy or musty water smell is rarely dangerous, but keeping your water system maintained ensures safe, fresh water for your home.
FAQs About Moldy-Smelling Water
1. Can I drink water that smells like mildew?
In most cases, yes—you can safely drink water that smells a bit musty or moldy, especially if the odor comes from naturally occurring compounds like geosmin or MIB. Your nose is extremely sensitive to these substances, so the smell can be noticeable even when the water is perfectly safe. However, if the musty smell lingers for days, worsens over time, or comes from a private well, it’s a good idea to get your water tested. Persistent odors can sometimes signal bacterial growth, sediment buildup, or other water quality issues. Running the taps, flushing your water heater, or using carbon filters can help improve taste and smell. When in doubt, contacting a certified water expert or local health authority ensures you’re drinking water that’s both safe and fresh.
2. How do I get rid of the mildew smell in water?
The first step is to tackle the most common sources at home. Clean your drains thoroughly, as mold or bacteria buildup there can contribute to a musty odor. Next, flush your water heater to remove sediment and microbial growth that may be causing the smell. Installing carbon filters—either at the faucet, pitcher, or as part of an RO system—can help remove organic compounds like geosmin and MIB that give water that earthy, mildew-like scent. If the odor persists despite these efforts, it’s important to test your water to check for bacterial contamination or other issues. Taking these steps ensures that your tap water not only smells fresh but is also safe to drink, giving you peace of mind every time you fill a glass.
3. Why does my cold water smell musty?
If your cold water has a musty or earthy smell, it’s usually not harmful but can be annoying. Most often, the culprit is biofilm—a slimy layer of bacteria and organic matter that forms inside pipes, especially in rarely used faucets. Another common source is compounds like geosmin or MIB present in the source water, which your nose can detect even at extremely low levels. Running taps for a few minutes can help flush out stagnant water and reduce the odor temporarily. For a longer-term solution, cleaning aerators, using point-of-use carbon filters, or having your plumbing checked can improve taste and smell. Persistent odors may require water testing to ensure safety, particularly for private wells or older plumbing systems.
4. Why does my sink water taste like mold?
If your sink water tastes moldy or musty, it’s usually not the water supply itself but rather mold or bacterial buildup in your drain or faucet aerator. These areas can trap moisture and organic material, creating the perfect environment for microbes to grow and affect the taste. To fix it, start by thoroughly cleaning the drain and removing the aerator—soak it in a mild disinfectant or vinegar solution to remove trapped buildup. Flushing the pipes by running cold and hot water for a few minutes can help clear stagnant water and improve flavor. In some cases, sediment in older pipes or hidden biofilm may also contribute to the off-flavor. For persistent issues, installing a point-of-use carbon filter or consulting a professional plumber can help ensure the water not only tastes fresh but is also safe to drink. Regular maintenance of drains and aerators is key to keeping your tap water tasting clean.
5. Why does shower water smell musty?
If your shower water has a musty or earthy odor, the problem usually comes from the hot water heater rather than the water supply itself. Over time, sediment can build up at the bottom of the tank, and bacteria may grow in the warm, low-oxygen environment, producing that unpleasant smell. To fix it, start by flushing the water heater according to the manufacturer’s instructions to remove sediment and debris. Replacing the magnesium anode rod with an aluminum one can also help reduce odors caused by chemical reactions. For stubborn or persistent smells, disinfecting the tank or consulting a water expert may be necessary. Running hot water regularly and performing annual maintenance can prevent future issues. These steps ensure your shower water smells fresh, feels clean, and is safe to use for bathing and other household needs.