Why does my water smell like rotten eggs or sulfur?
That rotten-egg smell is hydrogen sulfide gas — usually made by harmless bacteria in your water heater or in groundwater.
The likely causes
Produced by sulfur bacteria in the water or aquifer. It smells terrible at tiny concentrations but is generally not a health hazard at the levels found in homes.
If only the HOT water smells, the culprit is almost always bacteria reacting with the water heater’s magnesium anode rod — not your drinking water.
High sulfate groundwater can produce the smell and, at high levels, a laxative effect.
Is it dangerous?
Hydrogen sulfide is mostly an aesthetic (and very unpleasant) problem, not a poisoning risk at household levels. The main exceptions are very high sulfates. It is worth fixing because it is corrosive to plumbing and awful to live with.
How to tell what it is
Run the cold tap, then the hot. If only the hot water smells, it is your water heater — replacing the anode rod usually solves it. If both smell, the hydrogen sulfide is in the source water.
The fix
For whole-house hydrogen sulfide, a catalytic-carbon or oxidizing whole-house filter is the standard fix. For a hot-water-only smell, replace the water heater’s anode rod.
A small carbon pitcher will barely dent a strong sulfur smell — hydrogen sulfide needs a whole-house catalytic-carbon or oxidation system, or an anode-rod swap if it is only the hot water.
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