Why well water smells like rotten eggs, and what removes it

Where it comes from

Floridan aquifer water carries dissolved sulfate picked up from the rock it moves through. Where oxygen is absent, bacteria reduce that sulfate to hydrogen sulfide, and the gas comes out of the water at the tap. It is not a sign the well is contaminated by sewage, and it is not dangerous at the concentrations found in household wells. It is unpleasant, it tarnishes silver and copper, and it makes coffee taste wrong.

Why the hot taps are worse

Hot water releases the gas faster, so a shower smells stronger than a cold tap on the same supply. The water heater can also make its own: the magnesium anode rod inside many heaters reacts with sulfate to produce more sulfide. If the smell is only at the hot taps, the heater is the suspect and swapping the anode for an aluminium or powered one often ends it. If it is at every tap, the well water itself needs treatment.

Treatments that work

Aeration lets the gas escape before the water reaches the house. Oxidising filter media converts the sulfide to solid sulfur that the filter then traps and backwashes away. Chlorination followed by activated carbon oxidises the sulfide and strips the by-products. Which one suits a given well depends on the concentration, on whether iron is also present, and on the flow rate the house needs, all of which come from a lab test and a flow measurement.

What does not work

A carbon filter on its own is overwhelmed within weeks. A softener does nothing for sulfide and is fouled by it. Shock chlorinating the well removes the smell for a few days and it returns, because the source is the rock, not the well.