Musty odor after long periods of no use

Stagnant water after long non-use with musty odor

Quick Answer:

If a house or parts of its plumbing sit unused for months you can get a musty, stale smell from standing water, biofilm, or trapped debris. Open and flush every fixture, run appliances that use water, clean accessible traps and drains, and ventilate the space. If the smell persists or you see corrosion or discolored water, call a plumber.

Why This Happens

  • Standing water in pipes, traps, and appliances allows organic material and bacteria to grow, producing odors.
  • Dry traps allow sewer gas into the house; partially filled traps can go anaerobic and smell.
  • Residues in water heaters, washing machines, and dishwashers can concentrate smells when not used for a long time.
  • Poor ventilation and humid conditions let musty odors linger in rooms, carpets, and cabinetry.
  • Related issues can include mineral tastes or laundry smells—see Earthy taste after winterization and Musty odor in laundry water for more on similar problems.

Step-by-Step What to Do

1. Start with ventilation

  • Open windows and run exhaust fans to move stale air out.
  • Remove any wet or moldy materials (towels, rags, pails) from closets or appliances.

2. Flush all fixtures after extended vacancy

  • Turn on cold and hot taps at every sink, bathtub, and shower for several minutes each.
  • Flush every toilet at least once to refill the trap and move fresh water through the system.
  • Run outside hose faucets briefly to clear any standing water.

3. Run appliances that use water

  • Run a full cycle on the washing machine and dishwasher with detergent to clear hoses and internals.
  • Drain and refill the water heater if it has been idle for long periods or shows sediment.

4. Clean accessible traps and drains

  • Remove and clean removable drain strainers and shower/trap covers.
  • If a sink is slow or smells, remove the P-trap (place a bucket underneath) and clean it out.
  • Use a mechanical snake for persistent buildup; avoid pouring harsh chemicals into unfamiliar systems.

5. Treat and monitor

  • After flushing, note whether the odor fades. A mild sanitizing rinse (diluted bleach per product directions) can help on non-porous surfaces; rinse thoroughly.
  • Replace any small rubber seals, washers, or gaskets that show rot or odor retention.
  • If water appears cloudy, discolored, or has particles, collect a sample and consider professional testing.

6. Final checks

  • Verify all traps have water and are functioning.
  • Run outdoor drains and gutters to make sure moisture sources are not feeding the problem.
  • Repeat flushing and appliance runs over a couple of days if the building sat empty for months.

What Not to Do

  • Do not ignore long-stagnation odors — they indicate a source that needs attention and can worsen over time.
  • Do not pour large amounts of concentrated cleaners or drain chemicals into plumbing without knowing the system; they can damage pipes, septic systems, or fixtures.
  • Do not assume a quick spray of air freshener solves the underlying problem; it only masks the smell.

When to Call a Professional

  • If odors persist after flushing and cleaning, or if you have discolored water, visible corrosion, or sewage odors, contact a licensed plumber.
  • Call a professional if you suspect a broken trap, damaged sewer line, or if your home uses a septic system and smells strongly outdoors.
  • If you notice mold growth on building materials or a health reaction in occupants, consider a remediation specialist.

Safety Notes

  • When working on traps and drains, wear gloves and eye protection. Have a bucket and towels ready for spills.
  • If you use a sanitizer, follow label instructions and never mix bleach with ammonia or acidic cleaners.
  • When climbing to ventilate or inspect roofs and gutters, use safe footing and avoid risky maneuvers. Hire help for high or dangerous work.

Common Homeowner Questions

  • How long until the smell should be gone? If the source is simple (stale trap water or kitchen buildup) you may notice improvement within hours to a day after flushing; deeper problems may take longer or need a pro.
  • Can I disinfect plumbing myself? You can flush and use mild sanitizers on surfaces; avoid harsh chemicals inside plumbing without guidance.
  • Could the water be unsafe to drink? If water looks, smells, or tastes unusual after long stagnation, avoid drinking it and have it tested before regular use.

For more related articles, see the Musty, Earthy, or Moldy Water Smell hub.

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