Foul smelling water is caused by the combination of hydrogen, sulfur, and bacteria within the water. Sulfur and bacteria are naturally present within the water your appliances use, and that they won’t make you sick. When the magnesium anode rod in your water heater tank reacts with the sulfur and bacteria within the water, it creates enough hydrogen to make an odor. There are some ways to require care of this, from replacing the magnesium anode rod to purifying the water in your water heater.