That rotten egg smell in your well water is hydrogen sulfide — a naturally occurring gas that's easy to identify and fixable with the right system. Here's everything you need to know.
Hydrogen sulfide (H2S) is a dissolved gas that forms naturally in well water from sulfur-reducing bacteria or from geologic sources. At low concentrations (under 1 PPM) a carbon filter handles it. At moderate levels (1–8 PPM) an air injection system like the Springwell WF1 is the right tool. At high concentrations (8+ PPM) you need chemical injection.
If the smell is only in your hot water, the culprit is almost always the sacrificial anode rod in your water heater reacting with sulfur in the water. The fix is replacing the magnesium anode rod with an aluminum/zinc rod. This is separate from your well water treatment and costs about $30.
H2S testing requires a special field test — H2S dissipates quickly once water is drawn from the tap, so standard mail-in lab tests often miss it. Options:
| Trace amounts (under 0.5 PPM) | Carbon block filter — simple and inexpensive |
| Low to moderate (0.5–8 PPM) | Air injection oxidation — Springwell WF1 removes up to 8 PPM H2S |
| Moderate to high (5–15 PPM) | Peroxide injection + carbon filter — most reliable for high concentrations |
| Above 15 PPM | Chemical injection + aeration — professional system required |
Hydrogen sulfide is corrosive. At high concentrations it attacks copper pipes, brass fittings, and appliances — causing pinhole leaks and premature fixture failure. Beyond the infrastructure damage, the smell permeates laundry, cooking, and makes showering unpleasant. It's worth fixing.
If sulfur bacteria are the source, shocking the well with chlorine is a temporary fix that kills the bacteria. The smell returns within weeks to months as bacteria repopulate. Shock treatment is useful to confirm bacteria are the source, but permanent treatment requires a filtration system or UV sterilizer to prevent recolonization.