Have you ever gone to wash your face and noticed a bad smell, something like rotten eggs? What is
that smell and how can I get rid of it?
The incidence of rotten egg odor or black water in hot water lines is due to the reaction of sulfates and
micro-organisms in the water that create hydrogen sulfide (H2S). This is from the water not the water
heater. It is caused by a sulfate-reducing bacteria known as desulfovibrio. These bacteria cannot grow in
the presence of atmospheric oxygen, which is why they are not noticed in cold water, but when the water
is heated it becomes noticeable.
What is hydrogen sulfide, and how does it form?
Sulfur-reducing bacteria that are naturally present in ground water use sulfur as an energy source to
chemically change sulfites to produce H2S. The bacteria use sulfur from decaying plants, rocks, or soil.
They exist in environments that are oxygen-deficient, like deep wells and plumbing systems. However,
H2S can exist naturally in ground water as well. It can enter surface water through springs and quickly
escape into the atmosphere. Some of these waters have excessive sulfate content along with various
strains of sulfate-reducing bacteria. These bacteria, which are harmless to health, will react in stagnant
water that has been depleted from oxygen and will produce hydrogen sulfide gas, utilizing the hydrogen
ion from the anode (the rod in the water heater) cathode reaction. This is more common in softened water
containing sodium in place of calcium and magnesium. The anode may have some effect because of the
greater activity of the anode, the greater amount of the hydrogen ion and hydrogen sulfide gas. These
bacteria can be killed with adequate additions of chlorine such as chlorine feeder. This will usually
eliminate the problem.
How can H2S be treated?
There are two ways to eliminate the odor, the first is the easiest:
- Chlorination – by means of a continuous chlorine feeder; or periodic flushing with common
household bleach. This process is 100% effective only if the continuous chlorine feeder is installed. - Install a new anode rod after the water has been flushed with household bleach. This process may
not be 100% effective because without continuous chlorination, bacteria are still allowed to grow inside
the tank. The anode reduces the overall anode activity, therefore reducing the availability of hydrogen
ions.
How to chlorinate your water tank. - Turn off breaker to water heater or shut off the gas.
- Close the cold-water inlet valve.
- Open a nearby hot water faucet and the T & P (temperature and pressure) valve to relieve tank
pressure. - Drain the water enough to add bleach. Use a hose connected to the drain valve if an open drain is
not adjacent to the heater. - Remove the relief valve, anode rod or disconnect the hot water outlet pipe from the heater.
- Pour 1 gallon of bleach for every 30 gallons of water heater tank capacity. Use the relief valve,
anode rod or hot water outlet pipe opening. Re-pipe the water heater and close the T & P valve. - Open the cold water inlet valve at the heater and fill the tank with water. Observe the water level
through the closest hot water faucet. Close inlet valve when the tank is full. - Leave the bleach mixture in the heater for one hour.
- After one hour open all the water faucets and allow the bleach mixtures to clean the water supply
pipes. Drain the remaining bleach mixture from the tank through the heater drain valve. - Close the heater drain valve, make sure the cold water inlet is open, and completely fill the tank
with water. Wait 15 minutes. - Purge the hot water supply lines and drain, then drain the water through the heater drain valve.
Check the anode rod for serviceability; replace it with a new rod if any signs of deuterations. - Make sure you purge all the air out of the hot water lines from the hot water faucets. Then close
the faucets. - Check for any leaks at all fittings used. Fix any leaks.
- Make sure tank is full of water so you don’t burn out the top element if out of water. Then turn
breaker or gas back on. - Check for normal water heater operation
