Quick Answer:
If the first draw of water after a trip smells musty, it’s usually from stagnant water or surface growth in the pipes or fixtures. Start by flushing the lowest fixture in the house, then run cold and hot taps for several minutes and check aerators and filters. Avoid drinking that first-draw water until you’ve flushed and checked the system.
Why This Happens
- Water left sitting in pipes or in a water heater can develop mild microbial growth or pick up smells from biofilm on fixtures.
- P-traps that dry out in rarely used drains allow stale air into the home, which can smell musty when you run the tap.
- Activated carbon filters, new filter media, or disturbed deposits sometimes release an Earthy odor after filter change that can be mistaken for stale water.
- Warm, wet parts of the system (for example around a heater) can encourage odors if something has been disturbed or installed recently.
Step-by-Step What to Do
Flush the lowest fixture first after long absence.
Open the lowest sink, hose bib, or basement fixture and run cold water for several minutes until it clears and the smell fades. Starting low helps push stale water out of the whole system.
Run cold-water taps throughout the house
Open each cold tap one at a time and let it run for 2–5 minutes. Check for changes in smell and for any discoloration. If discoloration appears, run until water clears or use the lowest fixture to flush longer.
Run hot water and check the water heater
Run the hot taps after you’ve flushed cold water. If the hot water smells more than the cold, the water heater may be the source. Don’t attempt internal heater repairs unless you’re qualified.
Clean aerators, showerheads, and filters
- Unscrew aerators and rinse them; soak briefly in vinegar if they’re gunky.
- Replace or rinse point-of-use filters if installed. If a new or recently changed filter is suspect, reference advice on Moldy smell after water heater install for similar troubleshooting steps (filter and heater smells can overlap).
Run appliances and outdoor fixtures
Run the dishwasher, washing machine, and any outdoor hose bibs. These cycles help move fresh water through lines you may not use daily.
Recheck
After flushing and cleaning, smell the water again. If the musty smell is gone, it’s safe to use water normally. If it remains, proceed to the next section.
What Not to Do
- Do not consume first-draw vacation water.
- Don’t mix cleaning chemicals (for example, bleach and ammonia) when cleaning fixtures.
- Don’t attempt major water heater or plumbing repairs if you’re not trained; that can make problems worse.
When to Call a Professional
- The smell persists after thorough flushing and aerator/filter cleaning.
- Multiple outlets show persistent odor or discoloration, suggesting a supply or distribution issue.
- You suspect the water heater or a recent installation is the source—especially if you notice unusual tastes or health symptoms. Recent installations can create installation-related odors similar to a Moldy smell after water heater install.
Safety Notes
- If water is discolored, avoid drinking it until it runs clear. Use bottled water for drinking and cooking if in doubt.
- Wear gloves when cleaning aerators or handling cleaning chemicals, and ventilate the area.
- Avoid pouring large amounts of bleach into fixtures unless instructed by a professional; misuse can damage pipes, fixtures, or pose health risks.
Common Homeowner Questions
- Q: Is the water safe to drink after flushing?
A: If the smell is gone and water runs clear after several minutes of flushing, it’s generally safe; otherwise don’t drink it. - Q: How long should I run taps to clear the smell?
A: Typically 2–10 minutes per fixture; start at the lowest fixture and work upward. - Q: Could the municipal supply be the problem?
A: It’s possible but less common; check with neighbors or the water utility if the problem is widespread.
For more related articles, see the Musty, Earthy, or Moldy Water Smell hub.