Three Sources of the Rotten Egg Smell

1. Naturally occurring hydrogen sulfide in the aquifer. Some aquifers in Southern Maryland contain naturally occurring hydrogen sulfide gas. The smell is present in all water — hot and cold — and is consistent year-round. Treatment: aeration or an oxidizing filter (iron/sulfur filter).

2. Sulfur-reducing bacteria in the well. Sulfur-reducing bacteria convert sulfate in the water to hydrogen sulfide. The smell may be intermittent or worse after the well hasn't been used. Treatment: shock chlorination followed by continuous disinfection.

3. Anode rod reaction in the water heater. This is the most common cause in Maryland. The magnesium anode rod in your water heater reacts with sulfate in the water to produce hydrogen sulfide. The smell is only in hot water, not cold. Treatment: replace the magnesium anode rod with an aluminum/zinc rod.

The Maryland Well Water Context

In Calvert County and Anne Arundel County, the most common cause of rotten egg smell is the anode rod reaction — because the well water in this area has naturally high sulfate content. The fix is straightforward: replace the magnesium anode rod with an aluminum/zinc rod. This eliminates the smell without affecting water quality.

If the smell is in both hot and cold water, we test for hydrogen sulfide and sulfur bacteria before recommending treatment. The right treatment depends on the source — and treating the wrong source wastes money.