What Causes Sulfur Smell in Tap Water?

Updated July 19, 2017

A sulphur smell in tap water indicates a sulphur bacteria contamination in the residential water supply or treatment systems. The actual source of the odour is hydrogen sulphide gas, which is colourless with a foul egg odour. Also known as sewer gas, it is the waste product of sulphur digestion by sulphur-reducing bacteria. This bacteria thrives in oxygen-deficient and warm environments such as hot water heater tanks, water softener systems, wells and underground where groundwater may flow. The presence of hydrogen sulphide gas and sulphur bacteria can cause some mild health hazards and property damage. Treatment of sulphur bacteria contamination is dependent upon determining the source.

Well Water Supply

An overgrowth of sulphur-reducing bacteria can occur in the damp, low-oxygen environment of a water well. Naturally occurring sulphur from soil, rocks and decaying organic matter present in deep wells or where groundwater may flow is digested by sulphur-reducing bacteria releasing hydrogen sulphide gas into the water supply. A good indication of the well as the source of contamination is by the presence of the rotten egg smell in the cold and hot water tap. Treatment options for a contaminated well are aeration, installation of carbon filter, or chlorine treatment.

Hot Water Heater

Hot water heaters contain a metal rod known as an anode, or magnesium corrosion control rod. The purpose of this rod to self corrode to protect the water heater tank from corroding. The warm environment of the water tank promotes the growth of sulphur-reducing bacteria, which reacts with ions released from the rod as it corrodes producing hydrogen sulphide gas. An indication that the hot water heater is the source of bacteria contamination is by the presence of the rotten egg odour solely detected from the hot water tap. Treatment options are replacement of the anode rod, chlorine treatment or temporarily increasing water tank temperature to kill the bacteria.

Water Softner System

Water softeners use sodium ions to convert magnesium and calcium sulphate into sodium sulphate. Sulphur-reducing bacteria are halophilic, will grow in the brine tank of a water softener and will chemically react with the sulphate ions producing hydrogen sulphide gas. The water softener system is determined as the source of contamination by the presence of the sulphur odour in the treated water but not in the non-treated water. Treatments of bacteria contamination of the water softener are chlorine treatments, replacement of filter or sodium ion beads, or installation of a sulphate removal system.

Effects on Health and Plumbing Systems

Production of hydrogen sulphide in tap water sources is usually at low levels and considered more of nuisance than serious health risk due to the pungent odour and bitter taste it can give to the water. However, it can also cause diarrhoea, which can lead to dehydration with long periods of consumption. Extended exposure in confined spaces can also cause episodes of nausea. Hydrogen sulphide gas is also very corrosive to plumbing, metal piping, well housing and pump connections. Continuous growth of sulphur bacteria can develop into a black slime that can clog plumbing and filtration systems.

Prevention of Sulfur Bacterial Contamination

Regulatory maintenance and chlorine disinfection of residential water supply and treatment systems is a good way to control and reduce the occurrence of a bacteria contamination. Sulphur is naturally occurring in water. Therefore preventive measures are aimed toward minimising the growth of sulphur-reducing bacteria. In the event of a bacteria contamination, potential health risks can be reduced by limiting the use and consumption of the contaminated water through purchasing bottled water until the source of contamination has been detected and properly treated.

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About the Author

Shayla Perkins has a B.S. in biology and chemistry. She has worked in pharmaceutical research and development since 2001, and is currently working with the Vaccine Research Center at the National Institutes of Health and National Institute of Allergy and Infectious Diseases. Perkins' writing experience includes protocols, technical reports, intermediate synopsis and co-editing of journal submissions.