A rotten-egg smell usually comes from hydrogen sulfide gas or sulfur bacteria, often only in hot water from the water heater. A sewage smell can mean contamination, so stop drinking the water and test for bacteria. A metal taste or smell usually points to iron or manganese. A lab test tells you which you have.
Updated October 2026
Safety first: well pumps run on 230/240-volt circuits. Don’t open the pressure switch, control box or well cap wiring.
Hot, cold or both?
- Hot water only: the smell likely starts in the water heater. That’s a job for a licensed plumber.
- Hot and cold: the smell is likely in the well water itself.
- After a vacation: water that sat in the pipes can smell. Run the taps; if it doesn’t clear, test.
Why does my well water smell?
| Likely cause | What you can safely check | Needs a licensed pro? |
|---|---|---|
| Hydrogen sulfide in groundwater | Rotten eggs on hot and cold | Test; treatment is plumbing work |
| Water heater reaction | Rotten eggs on hot only | A licensed plumber |
| Sulfur or iron bacteria in the well | Slime in toilet tanks; worse after water sits | Yes, for disinfection |
| Sewage or septic contamination | Sewage or musty smell, often after rain | Stop drinking; test; yes |
| Iron or manganese | Metal taste, orange or dark stains | Test |
Why does my well water smell like sewage?
Treat it as possible contamination. Wisconsin DHS says a positive E. coli test means possible human or animal waste.
- Drink bottled water, or boil water for 1 minute, until a test comes back clean.
- Test for bacteria and nitrate. The State Lab of Hygiene charges $35 each (from July 1, 2026).
- Wisconsin code requires wells to sit at least 25 feet from a septic tank and 50 feet from a drainfield.
About disinfecting the well
Disinfection means opening the well cap near live wiring, so leave it to a licensed pro. Under rules revised March 1, 2026, a well that is still bacteria-positive after 3 failed batch chlorinations by a licensed driller or pump installer must be filled and sealed.
When you need a licensed professional
- A bacteria test is positive, or the smell is like sewage.
- The well cap or casing looks damaged.
- Treatment systems and water heaters: a licensed plumber, since pump installers’ work ends at the pressure tank.
Wisconsin rules require a DNR-licensed pump installer for pump and pressure-tank work on a drinking-water well; check with DNR if you’re unsure.
Related
- Coliform bacteria in your well
- Where to test well water
- Brown, orange or cloudy water
- Filling and sealing old wells
