Quick Answer:
A sudden rotten-egg smell usually means hydrogen sulfide gas in the water. Stop drinking the water, reduce use for cooking, and collect a sample from your well system for testing. If you have a pressure tank, Collect a well sample directly from the pressure tank drain. That sample is the most reliable for the source water.
Why This Happens
- Hydrogen sulfide gas (that rotten-egg odor) can form from sulfur-reducing bacteria or from chemical reactions with sulfate in the groundwater.
- Changes in water chemistry after heavy rain, well maintenance, or plumbing work can release trapped gas or encourage bacterial growth.
- Problems confined to hot water often point to the water heater—bacteria can grow there or an anode rod can react and create odors.
- Local or seasonal issues can cause sudden smells. For tips specific to isolated fixture smells, see Smell only in upstairs bathroom. For smells that started after closing or opening plumbing for winter, see Rotten smell after winterization.
Step-by-Step What to Do
1. Stop using water for drinking or cooking
- Use bottled or boiled water (boiling may not remove the smell and can concentrate minerals; bottled is safest until tests are back).
- Keep children and pets away from drinking untested well water.
2. Take a proper sample
- Collect a well sample directly from the pressure tank drain. This avoids plumbing fixtures that can mask the source.
- Turn off the pump at the breaker, open a drain or faucet to relieve pressure, then collect the sample in a clean container provided or recommended by your testing lab.
- Label the sample with date and time and get it to the testing lab or health department promptly, following their instructions.
3. Run simple checks at home
- Run cold water from a few taps for several minutes to see if the odor clears—this can help tell if it’s coming from a single fixture or the supply.
- Check whether the smell is only in hot water; if so, turn off the water heater and test cold water separately.
- Note any recent work on the well, pump, or plumbing that coincided with the smell.
4. Test the water
- Order a lab test for hydrogen sulfide, iron, sulfate, pH, and bacterial contamination (total coliform and E. coli).
- Follow the lab’s sample instructions exactly—sample location and handling matter for accurate results.
5. Follow treatment based on results
- If bacteria are present, the lab or local health office will advise whether shock chlorination is appropriate.
- For chemical causes (sulfate, iron), common fixes include aeration, filtration with catalytic media, or activated carbon systems—choose equipment after testing.
- If the water heater is the source, replacing the anode or flushing the heater may help; consult a plumber or appliance technician for safe service.
What Not to Do
- Do not shock the well without testing water chemistry.
- Do not assume the smell is harmless—hydrogen sulfide at high levels can be corrosive and some contamination means bacteria may be present.
- Do not use syringe drains, drain cleaners, or open well covers without proper training—those actions can be dangerous and contaminate the well.
When to Call a Professional
- Call a certified well professional or licensed plumber if the smell persists after flushing or if you’re unsure how to collect a proper sample.
- Call immediately if tests show coliform or E. coli bacteria, or if household members have symptoms like stomach upset after using the water.
- Get professional help for treatment options such as chlorination, aeration, or filter installation to ensure they’re done safely and to code.
Safety Notes
- Do not enter the well vault or lift a sealed well cap without training—wells can contain hazardous gases and are a fall risk.
- When performing any flushing or chlorination, ventilate the area and follow product safety instructions—bleach and chlorine can create harmful fumes.
- Keep bottled water on hand for drinking and cooking until lab tests confirm the water is safe.
Common Homeowner Questions
- Q: How fast can a lab return results?
A: Routine tests often take a few days; ask the lab for expected turnaround. - Q: Is the smell dangerous to breathe briefly?
A: Small amounts are unpleasant but usually not harmful; high concentrations can be irritating—leave enclosed areas if the smell is strong. - Q: Will flushing fix it?
A: Flushing can temporarily clear trapped gas, but it won’t fix bacterial or chemical causes—testing is needed.
For more related articles, see the Sulfur / Rotten Egg Smell in Water hub.