Bacteria

• Sulfur-reducing bacteria break down sulfur and create hydrogen sulfide gas. If they are living inside your hot water heater, this will cause the water inside the heater to smell like rotten eggs. When you run cool water in your home it will smell normal but when you run the hot water it will smell of sulfur.
  
  

Causes

• The magnesium rod inside your hot water heater can release anodes into the water there that sulfur-reducing bacteria can feed on. If you have turned off your hot water heater or keep it at a setting below 140 F, the bacteria can easily breed, according to the Nebraska Department of Health and Human Services.
  
  

Solution

• You can kill sulfur-reducing bacteria in your hot water heater by raising the temperature to 160 F. Leave it on high for eight hours, then drain the tank. This will flush the bacteria and the smell from the tank. Replacing the magnesium rod in the hot water heater with a zinc rod could help keep bacteria levels down in the heater in the future.