CWQA Position Statement

Hot Water and Rotten Egg Odour

To remedy rotten egg odours in hot water, any of the following methods may be used: 1) maintaining chlorine residuals; 2) flushing low-flow distribution lines; 3) killing bacteria with increased heat; 4) replacing magnesium anode rods with zinc; and 5) removing the cathodic-protection anode entirely.

 

Maintaining Chlorine Residuals

Marinating a chlorine residual of 1 mg/L throughout the distribution system oxidizes any hydrogen sulfide present and inhibits bacterial activity and corrosion associated with sulfate-reducing bacteria. In a non-chlorinated system, periodic disinfection and flushing of the water heater may be sufficient. If the problem is severe or persistent, a chlorine feeder system may be required.

 

Flushing Distribution Lines

Flushing of low-flow lines and looping of distribution lines to eliminate dead ends can reduce the concentration of the sulfate-reducing bacteria and help to alleviate the problems they cause.

 

Killing Bacteria with Heat

The thermal death point of sulfate-reducing bacteria is approximately 140F (60C). Water heaters are usually factory set at 140F +10F (60C+6C), which is the "meeting setting" on the temperature control dial. Increasing the temperature to the "high" setting (160F at 71C) for several hours and flushing the tank should kill the sulfate-reducing bacteria and greatly reduce the odour problem until the population of the bacteria becomes high again. CAUTION: The hot water tank must have an operable pressure relief valve; otherwise, this method of treatment may be dangerous. The temperature setting must be reduced following treatment to eliminate the risk of people being scalded from dangerously hot water and to avoid high energy costs.

 

Replacing Magnesium Anode Rods

Zinc has an electrode potential that is much closer to that of the steel tank than magnesium. If a zinc anode is used instead of magnesium, the zinc will sacrifice fewer excess electrons to reduce the sulfates. This remedy will not eliminate problems associated with sulfate-reducing bacteria, but it can greatly reduce them.

 

Removing Cathodic-Protection Anode

Removal of the cathodic-protection anode is not a preferred method, but it may alleviate the odour problem. This method eliminates all cathodic protection from the tank, which may shorten tank life.