Sulfur Water Control (Rotten Egg Odor in Home Water Supplies)

Foul-smelling or unusual odors from your water should make you question its quality and safety. Some odors indicate the presence of contaminants which may pose a health risk. Other odors, such as those caused by hydrogen sul- fide, are more of a nuisance, only affecting the taste of the water.

Effects of Sulfur Water

Sulfur in your water supply is easily recognized by its offensive odor. Hydrogen sulfide gas causes the "rotten-egg" or sulfur water smell. Hydrogen sulfide in water causes no known health effects. However, high concentrations do change the taste of the water.

Hydrogen sulfide dissolved in water corrodes metals such as iron, steel, copper and brass. The corrosion of iron and steel from sulfur forms ferrous sulfide or "black water." Hydrogen sulfide in water can blacken silverware and discolor copper and brass utensils.

Sulfur water makes cleaning clothes very difficult. Using chlorine bleach in sulfur water reduces the cleaning power of detergent. Hydrogen sulfide in water also corrodes exposed metal parts in washing machines.

Iron and manganese, often present with hydrogen sulfide, turn the water black and greasy-feeling. If untreated, the water stains laundry, washing machines, sinks and kitchenware. When used in the laundry, chlorine bleach reacts with iron and manganese forming dark rusty or brownish stains on clothes.

Occurrence & Characteristics

Generally, hydrogen sulfide occurs in concentrations of less than 10 mg/l (milligrams per liter), but occasionally amounts of 50 to 75 mg/l are found. Hydrogen sulfide is more commonly found in ground water supplies than in sur- face water. Hydrogen sulfide gas quickly escapes from surface water.

Wells drilled in shale or sandstone, or near coal or oil fields often have hydrogen sulfide present. Much of the ground water in northwestern and northeastern Indiana has noticeable hydrogen sulfide levels. High levels of hydrogen sulfide also occur in smaller sections around the state (Figure 1).

Figure 1. Areas of Indiana where hydrogen sulfide is found in ground water.

Hydrogen sulfide may also be produced when sulfate in well water converts to hydrogen sulfide. Certain non-disease-producing bacteria use the oxygen in the sulfate to form hydrogen sulfide.

Hydrogen sulfide causes the distinct, offensive odor of sewage. Occasionally, sewage pollution is the reason for the odor in drinking water. Sewage pollu- tion sulfide, and not a natural source, can occur in some surface water, in poorly constructed wells or in shallow wells close to sewer lines or septic tanks.

Under certain conditions, you may notice hydrogen sulfide when heating water. Heated water releases hydrogen sulfide gas quicker than cold water. A second situation occurs when sulfate in the water changes to hydrogen sulfide in the hot water heater. In this case, a magnesium rod has been installed in the water heater to reduce corrosion of the water heater. As the rod gives up small amounts of magnesium to the water, some hydrogen is released. The hydrogen can then combine with sulfur in the water and form hydrogen sulfide.

Hydrogen Sulfide Testing

The offensive odor of hydrogen sulfide generally makes testing unnecessary. Most people know when hydrogen sulfide is present and seek to correct the problem.

However, in a few cases, the odor may be from sewage pollution. Water with only hydrogen sulfide present does not cause disease. Sewage pollution, how- ever, contains disease-producing contaminants. When sewage pollution is a possible source of the sulfur, test your water for coliform bacteria.

Collect water samples for the hydrogen sulfide test at the well site. Hydro- gen sulfide gas easily escapes from water. Water testing labs and other pro- fessionals can provide further information on specific steps for testing.

Sulfide concentrations are reported as milligrams per liter (mg/l) or parts per million (ppm). These two terms are used interchangeably. Sulfide levels of 0.35 mg/l and less may go unnoticed. Amounts of 0.5 mg/l or more are usu- ally noticed, even in cold water. Some people become accustomed to the odor and tolerate hydrogen sulfide levels of 5 and 6 mg/l. Visitors might find such water very unpleasant, however.

Sulfur Removal Methods

Several methods of removing sulfur from water are available. The treatment method selected depends on many factors. These factors include the level of sulfur in the water, the amount of iron and manganese in the water, and if bacterial contamination must also be treated. Remember to consider the sim- plicity of the treatment method and the total cost including installation, maintenance and chemical costs.

Chlorine Bleach Removal Method

Chlorine bleach can effectively remove medium to high levels (over 6 mg/l) of hydrogen sulfide. The chlorine in the bleach chemically reacts with (oxi- dizes) the hydrogen sulfide eliminating the "rotten egg" odor. Chlorine bleach also reacts with iron or manganese, and disinfects water supplies.

An automatic chlorinator (chemical feed pump) adds chlorine to the water sys- tem (Figure 2). A filtering system then removes the sulfur, iron and man- ganese sediment formed. A settling tank sometimes replaces the filter system. A 500 to 1,000 gallon settling tank is generally sufficient.

Figure 2. Example of an automatic chlorinator system.

Depending upon the amount of chlorine bleach added, a dechlorinating carbon filter may be used to obtain chlorine-free water for cooking and drinking. The same activated carbon filter can also remove the sulfur sediment. Mainte- nance and replacement of filter systems should be considered since sulfur, iron, manganese and other suspended materials in the water soon clog the filter.

Iron Removal Filter Method

An iron removal filter can remove low to moderate amounts (up to around 10 mg/l) of hydrogen sulfide in addition to removing iron and manganese. The filter oxidizes the hydrogen sulfide, converting it into insoluble sulfur which the filtering process then removes.

The filter needs to be regularly recharged with potassium permanganate. The complex recharging process makes the filter system very specialized. The ins- tallation and operation instructions of the manufacturer should be followed precisely. Because the precipitated sulfur can clog the filter, the filter needs regular replacement.

Aeration Removal Method

Aeration (adding air to the water), by itself, may not always reduce the hydrogen sulfide to non-detectable levels. However, the process sometimes reduces the hydrogen sulfide to acceptable amounts.

An aerator is installed between the well and a non-pressurized water storage tank (Figure 3). A diffuser, cascade or spray aeration system above the tank aerates the incoming water. The release of the water pressure and exposure to the air removes some of the sulfur compounds. Oxidation removes some of hydrogen sulfide gas. The process does produce the strong hydrogen sulfide odor near the aerator.

Figure 3. Aeration releases hydrogen sulfide and provides an acceptable water supply for the household.

A corrosion-resistant, screened vent under a water-tight roof should be installed. The storage tank and aeration system must be secure to prevent contamination of the water supply.

Operation of the aeration system requires good ventilation. The tank needs occasional cleaning as precipitated sulfur, iron sulfide, rust and algae col- lect. A valve controlled drain line to the ground surface makes flushing the storage tank, once or twice each year, easier.

Besides reducing the sulfur content, aeration also helps remove some of the iron, if present in the water. Oxidation of the iron occurs, and with enough settling time (holding the water in the tank for two to three days), satis- factory odor-free and iron-free water can be obtained. Activated carbon filters

Activated carbon filters absorb some hydrogen sulfide but have very limited capacity for major odor absorption. Carbon filters commonly are installed under the sink to treat drinking and cooking water. The filters must be removed and replaced often.

Other Considerations

Ordinary household water softeners do not remove sulfur odors from water. In fact, softeners easily become fouled or clogged, reducing their softening capacity. The exchange material may eventually need replacing.

Drilling a new well to find water with lower sulfur content may be a solution or be a waste of effort and money. Changing the depth of the well or moving a distance away from the original well, may not result in tapping different water-bearing layers (Figure 4). A different water-bearing layer may or may not be sulfur-free. Generally, the deeper the well, the higher the mineral and sulfur content.

Figure 4. A new well may or may not have hydrogen sulfide in the water.

For Further Information

For further information on water quality contact your county Cooperative Extension office or local Health Department. The following bulletins in the WQ series may also be helpful:

WQ 1 "Water Testing Laboratories"
WQ 2 "What Is Ground Water?"
WQ 3 "How to Take a Water Sample"
WQ 4 "Why Test Your Water?"
WQ 5 "Interpreting Water Test Results Part One: Inorganic Materials"
WQ 6 "Buying Home Water Equipment"
WQ 9 "Water Quality for Animals"
WQ 10 "Wetlands and Water Quality"
WQ 12 "Distillation for Home Water Treatment"
WQ 13 "Home Water Treatment Using Activated Carbon"
WQ 14 "Reverse Osmosis for Home Treatment of Drinking Water"
WQ 16 "Bacterial Contamination of Household Water"


Clark, G. Douglas, ed., The Indiana Water Resource, Availability, Uses and Needs, Indiana Department of Natural Resources, Indianapolis, 1980, p. 86.

"Water Treatment Fundamentals", l983, Water Quality Association Educational Services.

Hydrogen Sulfide and Sulfur Bacteria in Well Water
Well Management Program

Hydrogen sulfide gas (H2S) can give water a “rotten egg” taste or odor. This gas can occur in wells anywhere and be:

  • Naturally occurring - a result of decay and chemical reactions with soil and rocks.
  • Produced by certain “sulfur bacteria” in the groundwater, well, or plumbing system.
  • Produced by sulfur bacteria or chemical reactions inside of water heaters.
  • From pollution (this is rare).

May Help Other Bacteria Grow

Sulfur bacteria produce a slime and can help other bacteria grow, such as iron bacteria. The slime can clog wells, plumbing, and irrigation systems.

Gas May be Harmful

While sulfur bacteria are not harmful, hydrogen sulfide gas in the air can be harmful at high levels. It is important to remove the gas from the water, or vent the gas to the atmosphere. Venting prevents the gas from collecting in low-lying spaces (such as well pits and basements) or enclosed spaces (such as well houses). Only well professionals should enter a well pit or other enclosed space where hydrogen sulfide gas may be present.

How to Detect

  • Bacterial slime may be white, grey, black, or reddish brown if associated with iron bacteria (signs of sulfur bacteria).
  • Black stains on silverware and plumbing fixtures (signs of hydrogen sulfide gas).
  • Corrosion on pipes and metal components of the water distribution system (signs of hydrogen sulfide gas).
  • Have your water tested at a laboratory.

Consider Testing Your Water

In most cases, the rotten egg smell does not relate to the sanitary quality of the water. In rare instances, the gas may be from sewage or other pollution. To be safe, test your well water for coliform bacteria and nitrate.

What You Can Do

The first step is to find out what the source of the issue is; that will let you know what treatment option is best.

How to Find the Source

After you have been away from your home for a few hours, smell the water coming out of the hot and cold water faucets. Determine which faucets have the “rotten egg” odor.

Flow chart decision tree. Is there a smell from the cold water faucet? If no, the problem is likely in the water heater. If yes, is there a smell from faucets not connected to the water softener? If no, the problem is likely sulfur bacteria in the water softener. If yes, is the smell less noticeable after the water runs for a few minutes? If no, the problem is likely hydrogen sulfide gas in the groundwater. If yes, the problem is likely sulfur bacteria in the well or plumbing system.

If the Problem is in the Water Heater

Unless you are very familiar with water heater operation and maintenance, have a plumber or water system professional to do the work.

  • Replace or remove the magnesium anode. Many water heaters have a magnesium anode, which is attached to a plug located on top of the water heater. It can be removed by turning off the water, releasing the pressure from the water heater, and unscrewing the plug. Be sure to plug the hole. Removal of the anode, however, may significantly decrease the life of the water heater. You may wish to consult with a water heater dealer to determine if a replacement anode made of a different material, such as aluminum, can be installed. A replacement anode may provide corrosion protection without contributing to the production of hydrogen sulfide gas.
  • Disinfect and flush the water heater with a chlorine bleach solution. Chlorination can kill sulfur bacteria. If all bacteria are not destroyed by chlorination, the problem may return within a few weeks.
  • Increase the water heater temperature to 160 degrees Fahrenheit (71 degrees Celsius) for several hours. This will destroy the sulfur bacteria. Flushing to remove the dead bacteria after treatment should control the odor problem.

CAUTION: Increasing the water heater temperature can be dangerous. Consult with the manufacturer or dealer regarding an operable pressure relief valve, and for other recommendations. Be sure to lower the thermostat setting and make certain the water temperature is reduced following treatment to prevent injury from scalding hot water and to avoid high energy costs.

How Hydrogen Sulfide Gas is Produced in a Water Heater

A water heater can provide an ideal environment for the conversion of sulfate to hydrogen sulfide gas. The water heater can produce hydrogen sulfide gas in two ways - creating a warm environment where sulfur bacteria can live, and sustaining a reaction between sulfate in the water and the water heater anode. A water heater usually contains a metal rod called an "anode," which is installed to reduce corrosion of the water heater tank. The anode is usually made of magnesium metal, which can supply electrons that aid in the conversion of sulfate to hydrogen sulfide gas. The anode is 1/2 to 3/4 inches in diameter and 30 to 40 inches long.

If the Problem is in the Well, Plumbing System, or Water Softener

Disinfect the well and plumbing system with a strong chlorine solution. You can hire a licensed well contractor to do this or refer to the Well Disinfection webpage for instructions.

Sulfur bacteria can be difficult to remove once established in a well. Pre-work (such as scrubbing the well casing, using special treatment chemicals, and agitating the water before disinfection) may be necessary—especially if there are also iron bacteria. Contact a licensed well contractor to do this pre-work.

If the bacteria are in the water softener or other treatment devices, contact the installer, manufacturer, or Minnesota Department of Health for disinfection instructions.

If the Problem is in Groundwater

Installing home water treatment or drilling a new well in a different formation are both options. Below are types of home water treatment effective at removing hydrogen sulfide gas. Learn more at the Home Water Treatment webpage.

  • Activated carbon filters are effective for hydrogen sulfide levels less than 1 milligram per liter (mg/L). The gas is trapped by the carbon until the filter is saturated. Since the carbon filter can remove substances in addition to hydrogen sulfide gas, it is difficult to predict its service life. Some large carbon filters have been known to last for years, while some small filters may last for only weeks or even days.
  • The following are options are effective for levels both below and above 1 mg/L.
    • Oxidizing media filtration (such as a manganese greensand filter) are effective for hydrogen sulfide levels up to about 6 mg/L. This type of treatment is often used to treat iron problems in water. The device consists of manganese greensand media, which is sand coated with manganese dioxide. The hydrogen sulfide gas in the water is changed to tiny particles of sulfur as it passes through the filter. The filter must be periodically regenerated, using potassium permanganate, before the capacity of the greensand is exhausted.
    • Aeration and filtration.
    • Continuous chlorination and filtration.
    • Ozonation and filtration.

Should I test my well water for anything besides hydrogen sulfide?

Yes. Both natural sources and human activities can contaminate well water and cause short-term or long-term health effects. Testing your well water is the only way to detect most of the common contaminants in Minnesota groundwater; you cannot taste, see, or smell most contaminants. Minnesota Department of Health recommends testing for:

  • Coliform bacteria every year and any time the water changes in taste, odor, or appearance. Coliform bacteria can indicate that disease-causing microorganisms may be in your water.
    See Bacterial Safety of Well Water.
  • Nitrate every other year. Bottle-fed infants under six months old are at the highest risk of being affected by levels of nitrate higher than 10 milligrams per liter in drinking water.
    See Nitrate in Well Water.
  • Arsenic at least once. About 40 percent of wells in Minnesota have arsenic in the water. Drinking water with arsenic in it for a long time can contribute to reduced intelligence in children and increased risks of cancer, diabetes, heart disease, and skin problems.
    See Arsenic in Well Water.
  • Lead at least once. The well and water system may have parts that have lead in them, and that lead can get into drinking water. Lead can damage the brain, kidneys, and nervous system. Lead can also slow development or cause learning, behavior, and hearing problems.
    See Lead in Well Water Systems.
  • Manganese before a baby drinks the water. High levels of manganese can cause problems with memory, attention, and motor skills. It can also cause learning and behavior problems in infants and children.
    See Manganese in Drinking Water.

Other contaminants sometimes occur in private water systems but less often than the contaminants listed above. Consider testing for:

  • Volatile organic chemicals if the well is near fuel tanks or a commercial or industrial area.
  • Agricultural chemicals commonly used in the area if the well is shallow and is near cropped fields or handling areas for agricultural chemicals or is in an area of geologic sensitivity (such as fractured limestone).
  • Fluoride if children or teenagers drink the water


First Check For Water Smells in Cold & Hot Water

The first step to finding out what to do when your water smells like rotten eggs is to see if the odor is from scorching water only, or if it is also coming from the cold well water.

Run a hose bib or tap as close to the well as possible and fill a 5-gallon bucket or other container and notice if there are odors.

If you smell a “rotten egg” odor, this is hydrogen sulfide gas. If the water smells like oil or asphalt this can be from manganese. If your water smells like cucumber or sewage this is usually a result of iron and/ or sulfur bacteria.

Run the hot water from each tap and notice if there is an odor in the hot water that is not apparent in the cold water.

If there is only an odor in the hot water, this indicates a problem with the water heater.

Sulfates in water, as well as iron and sulfur bacteria, can interact with the anode rod in water heaters.

This creates hydrogen sulfide gas which is the rotten egg smell in water. Changing the anode rod to an aluminum rod can often solve this problem of having well water that smells like sulfur.

If this is not convenient you can also hook up a “water heater odor killer” filter screen. This will also get rid of the sulfur smell in the water.

This device makes it easy to periodically add some store-bought hydrogen peroxide to the water heater, which kills the odor instantly and is safe to use.

Water Heater Sulfur Odors Only?

Read How to Eliminate Odors from Hot Water

Step 2: Test Your Water

If there is an odor problem with the water supply, the first step is to determine the source.

If the source of your water is a public water system and you have problems with smells in the cold water, contact your water utility, or call us for help.

If the source is from the well, a general mineral water analysis is critical to selecting the right system to treat the problem.

The test should include analysis for pH, iron, manganese, hardness, total dissolved solids at a minimum. Other tests for sulfate, hydrogen sulfide, and tannin are recommended as well.

Take the sample as close to the well as possible. With these results, you can identify the best type of water treatment to use, and what type of system to select, based on your water chemistry.

For health-related issues, your well water should be tested for total coliform and e-Coli (fecal coliform). If infants and children will be drinking the water, a general mineral, metals, and a bacteriological test is recommended.

Water Smells like Rotten Eggs: Choose a Method To Get Rid of Rotten Egg or Sulfur Smell in Water

ONE: If you have sulfur odor only in both cold and hot water, and no iron or manganese (rust, red or black staining) the best option is to use an Air Charger Carbon Filter with a peroxide cleaning kit (which comes as an option).

TWO: If you have extreme sulfur odors from the cold well water, we recommend shocking the well with chlorine and then installing a peroxide injection system with a backwashing carbon filter (see below).

THREE: If your well water smells like rotten eggs and you have iron in your water and rust staining, install a chlorinator followed by an iron filter.

FOUR: If you have rotten-egg sulfur smells in the hot water only, we recommend installing a Water Heater Odor Killer.

Use a Chlorinator or Inject Hydrogen Peroxide to Kill Odors

  • Use 5% grade liquid bleach or 12% liquid pool chlorine OR 7% hydrogen peroxide. The same system can inject either bleach or peroxide.
  • The precise dosage of chlorine or peroxide makes it easy to control.
  • The result is clean, fresh, disinfected, odor-free, chlorine-free water throughout your home.
  • Safe for septic tank systems
  • Works over a wide range of water flow rates for most home water wells
  • Good for chlorinating well water flow rates from 1 to 50 Gallons Per Minute (1 – 50 GPM)
  • Works for line pressures up to 110 PSI
  • Unlike Stenner-style or other types of peristaltic pumps, good quality diaphragm pump has no pump tube failures, no rollers to go bad, need less frequent service, and are good for continuous duty

Hydrogen sulfide gas (“H2S”), has a distinctive “rotten egg” sulfur smell, which may be especially noticeable when running hot water.

Such water can discolor coffee, tea, and other beverages, and alter the appearance and taste of cooked foods. Hydrogen sulfide (“H2S”) gas is a nuisance that is not usually a health risk at concentrations normally found in household water.

However, hydrogen sulfide can be toxic. Usually, the gas can be detected long before it reaches harmful concentrations. H2S is flammable and poisonous.

H2S dissolved in water can corrode plumbing metals, such as iron, steel, copper, and brass, and exposed metal parts in washing machines and other water-using appliances.

The corrosion of iron and steel from hydrogen sulfide forms ferrous sulfide or “black water” which can darken silverware and discolor copper and brass utensils.

Hydrogen sulfide can also interfere with the effectiveness of water softeners and filter systems.


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