Smelly or rotten-egg hot water

A rotten-egg or sewage smell in hot water is almost always hydrogen sulphide gas produced by bacteria living in the tank or the hot-water pipes. The bacteria need three things the tank provides: warmth, sediment to feed on, and water that has sat still, which is why the smell often appears in the first draw after the heater has been idle, or in homes with long runs and little use.

The usual treatments are practical rather than chemical: raising the tank temperature for a period to pasteurize the tank (with the mixing valve protecting fixtures at 49 °C), flushing sediment from the tank, and replacing the anode with one that does not feed the reaction. Some water supplies carry the sulphur precursors; a water test tells whether the smell is coming from the supply.

A rotten-egg smell is also the odour added to natural gas so leaks are detectable. The two are told apart by timing and place: a gas smell is constant near the appliance, appears when the heater is off, and is an emergency, while sulphide water smell comes from the taps and clears as the water runs. If there is any doubt, treat it as a gas leak: leave the building and call FortisBC at 1-800-663-9911 or 911.

Heat-pump water heaters pull air from the room through the evaporator, and a musty smell at the unit can come from the condensate pan or air path rather than the water. The condensate drain needs to flow freely and the air filter needs cleaning on units that have one, which the AeroTherm G2 sheet calls out with its filter alert.