Hydrogen Sulfide (H2S)

Hydrogen sulfide (H2S) is a colorless, flammable gas.   H2S gas is also called sewer gas, sour gas or stink damp.

Hydrogen sulfide gas occurs naturally in ground water.  The presence of hydrogen sulfide can be a result of a number of sources, such as:

  • Decomposing deposits of organic matter
  • Wells drilled in shale, sandstone, or near coal or peat deposits
  • Sulfur-reducing bacteria that feed on naturally occurring sulfates in water, producing the hydrogen sulfide gas.  While a nuisance, sulfur-reducing bacteria do not present any known human health risk.
  • Water heaters with magnesium rods.  The rods reduce the naturally occurring sulfates to hydrogen sulfide.
  • In rare cases, the gas may be a result of sewage or other wastewater pollution.  It is recommended that a coliform bacteria test also be performed.

Hydrogen sulfide gas produces an offensive “rotten egg” or “sulfur water” odor and taste in water.  The odor is noticeable when water is initially turned on or when hot water is running.  Heat forces the hydrogen sulfide gas into the air.  Most people can detect hydrogen sulfide in water by taste at concentrations as low as 0.05 ppm (mg/l) and by smell at concentrations as low as 0.1 ppm.  Some people can become used to both the odor and taste of hydrogen sulfide in water as high as 6 ppm.  Those that are not accustomed to sulfur water find it very unpleasant.

Water supplies with concentrations of 1.0 ppm of hydrogen sulfide may be corrosive to iron, steel, copper, and brass.  It can tarnish silverware and discolor copper and brass utensils.  It can also cause yellow or black staining on kitchen and bathroom fixtures.  It can also affect the taste of cooked foods and beverages (such as coffee and tea).  Higher concentrations of hydrogen sulfide may foul the resin bed of an ion exchange water softener.                                                                                                                                                                                                                                                                 HEALTH EFFECTS
No health effects have been found in humans exposed to typical environmental concentrations of hydrogen sulfide (0.00011– 0.00033 ppm) in air. Very little information is available about health problems that could occur from drinking or eating something with hydrogen sulfide in it. Scientists have no reports of people poisoned by such exposures. Hydrogen sulfide has not been shown to cause cancer in humans.

Hydrogen sulfide gas can irritate the eyes, nose and throat. Eyes may become watery, red and itchy. Exposure to H2S can also cause headaches, nausea (upset stomach), fatigue (feeling tired), shortness of breath, chest pain and other health-related symptoms. Brief exposures to high concentrations of hydrogen sulfide in air (greater than 500 ppm) can cause a loss of consciousness.

Most people can smell H2S at levels much lower than the levels that can cause these health effects. Just because you smell H2S, does not always mean you will experience adverse (bad/negative) health effects. However, sensitive populations, infants, young children, the elderly, people with asthma or other respiratory problems and people with heart problems may be more likely to experience these symptoms and negative health effects from exposure to H2S. 

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Hydrogen Sulfide (H2S)

Contaminant group: 
Major sources in drinking water: 
Naturally in some groundwater. Often present in wells drilled in shale or sandstone, or near coal or peat deposits.
Treatment options: 

Hydrogen sulfide can be easily removed from drinking water. The most common approaches are listed below.

  • If the odor is only from the hot water system and if there are magnesium corrosion protection rods, then an easy solution may be to permanently remove the rods. Where the water is corrosive, substituting aluminum protective rods for the magnesium is suggested. Replacement or removal of these rods, however, may void the tank warranty. Check with your hot water tank dealer.
  • Granular Activated Carbon (GAC)/Adsorption: If you have trace amounts (0.05-0.3 ppm), installing an activated carbon filter will reduce the unpleasant taste but it has limited capacity for odor adsorption.   In this process water is passed through granular activated carbon (GAC). The taste/odor components are taken up and held on the interior surfaces of the carbon particles as the water passes through. A granular filter must backwashed periodically; a cartridge filter must be cleaned or replaced periodically.  These filters can also remove chlorine, tannins, and other dissolved organic compounds.  If intending to use GAC, also test the water for radionuclides.
  • Aeration: Aeration is effection for levels less than 2.0 ppm.  In this process large volumes of air are blown through the water. The hydrogen sulfide volatilizes into the air bubbles. The “used” air is then vented outside the home. Aeration is also beneficial in removing radon gas and in raising the water's pH by allowing the “off-gassing” of excess carbon dioxide. The principal disadvantage of this method is possible bacterial growth in the treated water caused by the use of dirty air. Off-gassing of the hydrogen sulfide will be less complete where the pH of the water is high. 
  • Iron Removal Filter:  Iron removal filters should be considered when levels are between 1.0 and 10.0 ppm.  This method uses manganese greensand to remove low to moderate levels of hydrogen sulfide in addition to iron and manganese through oxidation. Once the oxygen is depleted, the filters must be recharged with a solution of potassium permanganate.  This process is very similar to water softener regeneration processes and must be done at regular intervals depending on the water chemistry, unit size, and amount of water to be processed. 
  • Oxidation: This method is recommended when levels are up to 75 ppm.  In this method an oxidizer (potassium permanganate, chlorine or ozone) is added to the water.  This process is followed by a filter to remove taste or sediment when hydrogen sulfide concentrations are 6.0 ppm or more. The oxidizer chemically reacts with the odor compounds so as to destroy the odor.  It takes 3 parts of chlorine to treat 1 part of hydrogen sulfide. One relatively low cost variation on this process uses a Venturi nozzle to add small amounts of air to the water. Air contains approximately 20 percent oxygen. The water then proceeds to a detention tank that provides both chemical reaction time and also allows for air release for the unused air.
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