Why Does My Water Smell Like Sulfur or Rotten Eggs?

Water from the tap, especially the hot side, gives off a smell reminiscent of rotten eggs. It's unpleasant, but generally not dangerous, and the cause is almost always fairly easy to identify.

Where the smell comes from

The smell almost always comes from bacteria producing hydrogen sulfide, a gas with a distinctive odor, reacting with the sacrificial anode inside the water heater — a metal rod designed to attract corrosion and protect the tank. This reaction happens mostly in water heaters left unused for long stretches or with certain water types, particularly well water.

Why usually just the hot water

How to confirm it's the water heater

Fill a glass with cold water straight from the tap and smell it, then do the same with hot water. If only the hot water carries the smell, the water heater is almost certainly the cause rather than the water source itself.

Fixes

Disinfecting the tank with a hydrogen peroxide solution, done by a professional, generally eliminates the responsible bacteria effectively. In some cases, replacing the standard magnesium sacrificial anode with an aluminum-zinc anode reduces the chemical reaction producing the smell, a more lasting fix than disinfection alone.

When to worry more

If the smell is present in cold water too, or accompanied by a change in the water's color or taste, the cause could be tied to the water source itself rather than the water heater — a situation that warrants a full water test, particularly for a property on a well.