Why does my hot water smell like rotten eggs?

Run the cold tap and smell it, then the hot. If only the hot water smells, the cause is almost always in the hot water system. If the cold water smells too, the problem is in the supply, so contact your water retailer before anyone touches the tank.

Then separate a smell in the water from a smell in the air. Natural gas has a rotten egg odour added on purpose so leaks get noticed. If you smell it around a gas water heater, heater or cooktop rather than from the tap, treat it as a possible gas leak, not a water problem.

Most storage tanks have a sacrificial anode, a metal rod that corrodes so the tank lining doesn't. Some bacteria found naturally in water feed on sulphates, and the reaction around the anode produces hydrogen sulphide, the gas behind the smell. A tank left unused while you were away, a household that uses very little hot water, or a tank that isn't reaching its normal temperature all give the bacteria a better chance.

That last cause is often electrical. If the element or thermostat in an electric tank has failed, or an off-peak supply isn't switching on properly, the water can sit lukewarm for days. Our team tests the element, thermostat and circuit, so you know whether the tank is heating as it should.

A licensed plumber can flush the tank, fit an anode that suits your water and check the valves. Opening a tank, removing an anode or changing the temperature settings isn't a DIY job: the system holds water under pressure at scalding temperatures, and electric tanks have live parts behind their covers.

A smell on its own doesn't mean the tank is finished. Rusty or discoloured hot water, water around the base, or an older tank whose anode has never been changed all point that way. If the tank is near the end, replacing it on your own timing beats waiting for it to fail, and it's the moment to look at whether a heat pump suits your home.