The sulphur or rotten egg smell and/or taste of water comes from a concentration of hydrogen sulphide gas. The hydrogen sulphide gas can occur naturally in groundwater, be produced by sulphur bacteria, be caused by a chemical reaction within a water heater or come from pollution. The type of treatment to get rid of the smell depends on the source.
Is it Harmful?
The sulphur smell and/or taste is generally not a sanitary concern. The only time it is a concern is when it is a result from pollution or sewage. Well water should be tested for nitrate and coliform bacteria. The sulphur bacteria itself is not harmful nor is a small level of hydrogen sulphide gas. The problem occurs when the hydrogen sulphide gas collects in large volumes. The sulphur bacteria either needs to be removed from the water or the gas needs to be vented into the atmosphere so it does not collect in low lying spaces.
Slime is produced by sulphur bacteria. The slime is a good breeding ground for bacteria. The main bacteria that will form is an iron bacteria. Iron bacteria can be black, reddish brown, white or grey. The sulphur bacteria slime is thick and can cause clogs in the plumbing, wells, drainage and irrigation systems. An iron bacteria growing in the slime will cause black staining that is noticeable on plumbing fixtures and silverware.
Hydrogen sulphide gas is formed through the decay of organic matter. It can also be formed by the chemical reaction of water to minerals that contain sulphur within the ground. The water then carries the sulphur to the water holding area. Sulphur bacteria releases the hydrogen sulphide gas from the water.
A water heater produces hydrogen sulphide gas in two ways. The anode used to prevent corrosion within the water heater is made of magnesium. The magnesium metal charges the electrons in the water which can release the hydrogen sulphide gas. The heating of the water inside a water heater creates a warm environment where sulphur bacteria can live. The sulphur bacteria reacts with the magnesium anode and helps to create the hydrogen sulphide gas.
Locating the Source
Checking for the sulphur or rotten egg smell should be done after an absence from the home for several hours. Pour a glass of cold water first and smell the contents then pour a glass of hot water and do the same. If the hot water is the only glass of water that smells then the problem is most likely the hot water heater. If a water softener is present in the home, the same process should be completed to see that water has the odour of sulphur. If the soft water is the only one that has the odour of sulphur then water softener is the problem.
Sulphur bacteria in the well or distribution system is most likely the case when the sulphur order is strongest when the water is turned on but diminishes after the water has been running a few minutes. Hydrogen sulphide gas in the groundwater is most likely the case if the sulphur order stays constant whether the water is just turned on or has been running for several minutes.