Sulfate, Hydrogen Sulfide, Sulfate Reducing Bacteria - How to Identify and Manage


Two forms of sulfur are commonly found in drinking water supplies: sulfate and hydrogen sulfide. Both forms are nuisances that usually do not pose a health risk at the concentrations found in domestic water supplies.


Sulfates and Hydrogen Sulfide

Sulfates are a combination of sulfur and oxygen and are a part of naturally occurring minerals in some soil and rock formations that contain groundwater. The mineral dissolves over time and is released into groundwater.

Sulfur-reducing bacteria, which use sulfur as an energy source, are the primary producers of large quantities of hydrogen sulfide. These bacteria chemically change natural sulfates in water to hydrogen sulfide. Sulfur-reducing bacteria live in oxygen-deficient environments such as deep wells, plumbing systems, water softeners and water heaters. These bacteria usually flourish on the hot water side of a water distribution system.

Hydrogen sulfide gas also occurs naturally in some groundwater. It is formed from decomposing underground deposits of organic matter such as decaying plant material. It is found in deep or shallow wells and also can enter surface water through springs, although it quickly escapes to the atmosphere. Hydrogen sulfide often is present in wells drilled in shale or sandstone, or near coal or peat deposits or oil fields.

Occasionally, a hot water heater is a source of hydrogen sulfide odor. The magnesium corrosion control rod present in many hot water heaters can chemically reduce naturally occurring sulfates to hydrogen sulfide.


Sulfate minerals can cause scale buildup in water pipes similar to other minerals and may be associated with a bitter taste in water that can have a laxative effect on humans and young livestock. Elevated sulfate levels in combination with chlorine bleach can make cleaning clothes difficult.  Sulfur-oxidizing bacteria produce effects similar to those of iron bacteria. They convert sulfide into sulfate, producing a dark slime that can clog plumbing and/or stain clothing. Blackening of water or dark slime coating the inside of toilet tanks may indicate a sulfur-oxidizing bacteria problem. Sulfur-oxidizing bacteria are less common than sulfur-reducing bacteria.

Hydrogen Sulfide

Hydrogen sulfide gas produces an offensive "rotten egg" or "sulfur water" odor and taste in the water. In some cases, the odor may be noticeable only when the water is initially turned on or when hot water is run. Heat forces the gas into the air which may cause the odor to be especially offensive in a shower. Occasionally, a hot water heater is a source of hydrogen sulfide odor. The magnesium corrosion control rod present in many hot water heaters can chemically reduce naturally occurring sulfates to hydrogen sulfide.

A nuisance associated with hydrogen sulfide includes its corrosiveness to metals such as iron, steel, copper and brass. It can tarnish silverware and discolor copper and brass utensils. Hydrogen sulfide also can cause yellow or black stains on kitchen and bathroom fixtures. Coffee, tea and other beverages made with water containing hydrogen sulfide may be discolored and the appearance and taste of cooked foods can be affected.

High concentrations of dissolved hydrogen sulfide also can foul the resin bed of an ion exchange water softener. When a hydrogen sulfide odor occurs in treated water (softened or filtered) and no hydrogen sulfide is detected in the non-treated water, it usually indicates the presence of some form of sulfate-reducing bacteria in the system. Water softeners provide a convenient environment for these bacteria to grow. A "salt-loving" bacteria, that uses sulfates as an energy source, may produce a black slime inside water softeners.

Health Issues


Sulfate may have a laxative effect that can lead to dehydration and is of special concern for infants. With time, people and young livestock will become acclimated to the sulfate and the symptoms disappear. Sulfur-oxidizing bacteria pose no known human health risk.  The Maximum contaminate level is 250 mg/L.

Hydrogen Sulfide

Hydrogen sulfide is flammable and poisonous. Usually it is not a health risk at concentrations present in household water, except in very high concentrations. While such concentrations are rare, hydrogen sulfide's presence in drinking water when released in confined areas has been known to cause nausea, illness and, in extreme cases, death. Water with hydrogen sulfide alone does not cause disease. In rare cases, however, hydrogen sulfide odor may be from sewage pollution which can contain disease-producing contaminants.   Therefore, testing for bacterial contamination and Sulfate Reducing Bacteria is highly recommended.

Testing Options


The Option 1 testing kit includes the sulfate test, but for sulfur problems the laboratory must be notified to provide a special container that has a chemical preservative.   The testing kits include the sampling instructions, a questionnaire, and information on returning the sample. Hydrogen Sulfide- If this is a problem that laboratory must be told in advance to provide the necessary sampling container with preservatives.

Since hydrogen sulfide is a gas that is dissolved in water and can vaporize (escape) from it, laboratory analysis of hydrogen sulfide in water requires the sample be stabilized immediately following collection. Since the odor may be caused by a number of factors, it is critical that the questionnaire be completed and it is highly recommended that both the Option 1 and Option 3 water testing packages are conducted..

Drinking Water Standards


The Environmental Protection Agency (EPA) standards for drinking water fall into two categories -- Primary Standards and Secondary Standards.  Primary Standards are based on health considerations and are designed to protect people from three classes of toxic pollutants -- pathogens, radioactive elements and toxic chemicals. Secondary Standards are based on taste, odor, color, corrosivity, foaming and staining properties of water. Sulfate is classified under the secondary maximum contaminant level (SMCL) standards. The SMCL for sulfate in drinking water is 250 milligrams per liter (mg/l), sometimes expressed as 250 parts per million (ppm).

Hydrogen Sulfide

Although many impurities are regulated by Primary or Secondary Drinking Water Standards set by the EPA, hydrogen sulfide is not regulated because a concentration high enough to be a drinking water health hazard also makes the water unpalatable. The odor of water with as little as 0.5 ppm of hydrogen sulfide concentration is detectable by most people. Concentrations less than 1 ppm give the water a "musty" or "swampy" odor. A 1-2 ppm hydrogen sulfide concentration gives water a "rotten egg" odor and makes the water very corrosive to plumbing. Generally, hydrogen sulfide levels are less than 10 ppm,  but have been reported as high as  50 to 75 ppm.

The Options

If excessive sulfate or hydrogen sulfide is present in your water supply, you have three basic options: 

1) Obtain an alternate water supply, bottled water,  or use some type of treatment to remove the impurity. The need for an alternate water supply or should be established before making an investment in treatment equipment or an alternate supply. Based the decision the results of a chemical analysis water, by a reputable laboratory, and after consulting with your physician to help you evaluate the level of risk.  It may be possible to obtain a satisfactory alternate water supply by drilling a new well in a different location or a shallower or deeper well in a different aquifer.

2)Another alternate source of water is bottled water that can be purchased in stores or direct from bottling companies. This alternative might be considered especially when the primary concern is water for food preparation and drinking.

3)The typical recommendation is the installation of a whole-house treatment system.  The section of the most cost effective system is a function of the overall water quality, cause of the sulfur odor, and other water treatment issues.

Sulfate Treatment

Several methods of removing sulfate from water are available. The treatment method selected depends on many factors including the level of sulfate in the water, the amount of iron and manganese in the water, and if bacterial contamination also must be treated. The option you choose also depends on how much water you need to treat.

For treating small quantities of water (drinking and cooking only)  the typical methods may be distillation or reverse osmosis. The most common method of treating large quantities of water is ion exchange. This process works similar to a water softener. Ion-exchange resin, contained inside the unit, adsorbs sulfate. When the resin is loaded to full capacity with sulfate, treatment ceases. The resin then must be "regenerated" with a salt (sodium chloride) brine solution before further treatment can occur.

Distillation boils water to form steam that is then cooled and then recondense the water. Minerals, such as sulfate, do not vaporize with the steam and are left behind in the boiling chamber.  Reverse osmosis membranes have a porosity that permits water molecules to pass through but leaves the large ions in solution.

Hydrogen Sulfide

Hydrogen sulfide may be temporarily controlled by conducting a shock chlorination / disinfection of the well or water source.  Please visit the  Shock Chlorination page to get more information on this protocol.  If the problem with the well is because of Sulfate Reducing Bacteria, a high level of chlorination, mixing, and turbulence may be needed.

If hydrogen sulfide odor is associated primarily with the hot water system, a hot water heater modification may reduce the odor. Replacing the water heater's magnesium corrosion control rod with one made of aluminum or another metal may improve the situation.

To remove low levels of hydrogen sulfide, install an activated carbon filter. The filter must be replaced periodically to maintain performance. Frequency of replacement will depend on daily water use and concentration of hydrogen sulfide in the water.

Hydrogen sulfide concentrations up to about 5 to 7  ppm can be removed using an oxidizing filter.  These filters are similar to the units used for iron treatment . This filter contains sand with a manganese dioxide coating that changes hydrogen sulfide gas to tiny particles of sulfur that are trapped inside the filter. The sand filter must be backwashed regularly and treated with potassium permanganate to maintain the coating.  Hydrogen sulfide concentrations exceeding 7 to 10 ppm can be removed by injecting an oxidizing chemical such as household bleach or potassium permanganate followed up by filtration. The oxidizing chemical should enter the water upstream from the storage or mixing tank to provide at least 30- 45  minutes of contact time between the chemical and water. The length of the holding time is a function of the chemical dosage, tank configuration, and water temperature.  Sulfur particles can then be removed using a sediment filter and the excess chlorine can be removed by activated carbon filtration. When potassium permanganate is used a manganese greensand filter is recommended.

Often the treatment for hydrogen sulfide is the same as for iron and manganese, for more information please visit the iron and manganese webpage.

Nuisance Problems

Sulfates and hydrogen sulfide are both common nuisance contaminants. Although neither is usually a significant health hazard, sulfates can have a temporary laxative effect on humans and young livestock. Sulfates also may clog plumbing and stain clothing.  Hydrogen sulfide produces an offensive "rotten egg" odor and taste in the water, especially when the water is heated.  If the odor is stronger in the hot water, we recommend the following:

a. Turn off the system and drain the tank.  Note any anolomies, such as: the color and odor of the water, coatings, precipitates, or other solid materials.
b. Allow the tank to refill, but raise the temperature setting of the tank to a level above 140 F.
c. Allow the tank to stay at this level for at least 6 to 10 hours.
d. Turn off the system and reduce system to the normal temperature setting.
e. Drain any discolored water and then allow the tank to refill.
f. If the odor goes away, it was most likely a bacteria growing in the tank that is causing the problem.
g. If the odor returns immediately, it is likely a chemical reaction between the water and the sacrifical anode used in the system.  It would be advisable to check the quality of the entering the tank.

If you have a well, we recommend that you also shock disinfect the well and distribution system.  For guidance on disinfecting a water heater, go here.

Treatment options depend on the form and quantities in which sulfates and/or hydrogen sulfide occur in untreated water- Therefore, it is critical that a comprehensive water analysis be conducted.. Small quantities of sulfate may be removed from water using distillation or reverse osmosis, while large quantities may be removed using ion exchange treatment.  Hydrogen sulfide gas may be associated with the presence of Sulfate Reducing Bacteria. Hydrogen sulfide may be reduced or removed by shock chlorination, water heater modification, activated carbon filtration, oxidizing filtration or oxidizing chemical injection. Often treatment for hydrogen sulfide is the same as for iron and manganese, allowing the removal of all three contaminants in one process.  

Note: If the cause of the problem is associated with the presence of Iron Reducing Bacteria, Sulfate Reducing Bacteria, and elevated levels of hydrogen sulfide, iron, manganese and other problems. It is critical that the water be tested prior to selecting a treatment system, we recommend the Water Testing .   Also, if you plan to shock disinfect your well or distribution system - we recommend using Sanitizing Pellets (Well Safe) over bleach.

Staining in Dishwasher and Selecting a Detergent
How to Shock Disinfect a Well
Odor Problems, Cause, and Action
Odors in Hotwater and Sulfur (Rotten Egg Odors)

Well Biofouling
Treatment for Sulfur Odors (No Bacterial Origin)

Online Training Courses

New Online Training Courses for Professional
LEED- AP / Green Associate Training/
Professional Development Hours Courses