Hydrogen sulfide is a gas that is produced naturally by decomposing organic material and sulfur-reducing bacteria. Hydrogen sulfide gives water a nuisance “rotten egg” smell and taste. While there is no federal drinking water quality standard set for hydrogen sulfide in water, water supplies with 1.0 milligram per liter (mg/L) of hydrogen sulfide may be corrosive and tarnish copper pipes and fixtures. Sulfides can produce yellow or black stains on kitchen and bathroom fixtures and can affect the appearance and taste of some foods and beverages. Treatment options for hydrogen sulfide include aeration, granular activated carbon filtration, and chlorination to kill the sulfur-producing bacteria.
Sulfates are part of naturally occurring minerals contained within soil and rock formations. As water percolates down through the soil, these minerals can dissolve releasing sulfates into groundwater. The Secondary Maximum Contaminant Level (SMCL) for sulfate in drinking water is 250 mg/L as established by the Environmental Protection Agency. Please note, the SMCL is a recommended maximum concentration based on the aesthetic quality of the water as opposed to a required maximum concentration.
Potential Health Effects
Hydrogen sulfide gas is flammable and poisonous at high concentrations. Buildup of hydrogen sulfide concentrations in a confined area has been known to cause adverse health effects in workers. However, the nose is very sensitive to the foul odor of hydrogen sulfide and under normal environmental conditions, this early warning sign provides protection from even mild health effects such as irritation.
Water with dissolved hydrogen sulfide gas alone does not cause disease. In rare cases, however, hydrogen sulfide odor may be from sewage pollution that can contain disease-causing contaminants. Therefore, arrange to test the water for bacterial contamination if sewage is the likely source of hydrogen sulfide. You may also want to test your well water for detergents if sewage contamination is suspected.
Elevated sulfate levels in water may have a laxative effect that can lead to dehydration and is mostly a concern for infants. High sulfate levels can be a result of sulfur oxidizing bacteria present in the water supply. While they can be a nuisance, sulfur-oxidizing bacteria do not present any known human health risk.
Indication of Hydrogen Sulfide and Sulfate in Drinking Water
• Hydrogen sulfide gas produces an offensive “rotten egg” odor in the water.
• Most people can detect hydrogen sulfide in water at concentrations as low as 0.5 mg/L.
• Concentrations less than 1 mg/L gives water a “musty” or “swampy” odor.
• A concentration of 1-2 mg/L gives water the “rotten egg” smell and makes it very corrosive to household plumbing.
• The odor may be noticeable only when the water is initially turned on or when hot water is running. Heat forces the hydrogen sulfide gas into the air, which may cause the odor to be particularly offensive in the shower.
• Hydrogen sulfide is corrosive to metals, such as iron, steel, copper, and brass. It can tarnish silverware and discolor copper and brass utensils. It can also cause yellow or black stains on kitchen and bathroom fixtures.
• Coffee, tea and other beverages made with hydrogen sulfide contaminated water may be discolored and the appearance and taste of cooked foods can be affected.
• High concentrations of dissolved hydrogen sulfide can foul the resin bed of an ion exchange water softener. When hydrogen sulfide odor occurs in treated water and was not originally detected in the pre-treated water, it indicates the presence of sulfate-reducing bacteria in the treatment system.
• Sulfates can cause a scale buildup in water pipes like other minerals. It may be associated with a bitter taste in the water. While not as common, another bacterium known as sulfur-oxidizing bacteria feeds on sulfides, which converts it to sulfates. This can result in a dark slime that can clog plumbing and stain clothing.
Sources of Hydrogen Sulfide and Sulfate in Drinking Water
Hydrogen sulfide gas occurs naturally in groundwater and can result from several sources.
• Decomposing underground deposits of organic matter such as decaying plant material can produce hydrogen sulfide.
• Wells drilled in shale or sandstone or near coal or oil fields or peat deposits may also be sources of hydrogen sulfide.
• Sulfur-reducing bacteria feed on the naturally occurring sulfates in water, producing hydrogen sulfide gas as a by-product.
Testing for Hydrogen Sulfide and Sulfate in Private Drinking Water Wells
Since hydrogen sulfide is detectable by taste and smell, determining its presence in drinking water does not normally require a laboratory test. However, it is necessary to determine the amount of hydrogen sulfide in the water to determine which treatment method will be most effective; therefore, testing is needed to quantify the levels of hydrogen sulfide.
To determine the level, arrange to test your drinking water at a state certified laboratory. Follow the laboratory's instructions carefully to obtain a representative sample and to avoid contamination. The water sample must be chemically stabilized immediately after collection, since hydrogen sulfide is a gas that can easily escape from the sample. Be sure to obtain the proper sample bottle, chemical preservative and instructions from the laboratory. If sewage pollution is the suspected source of contamination, also collect a separate sample to test for bacteria. You may also want to collect an additional sample to test for detergents. Consult with your environmental laboratory on the appropriate sample collection procedures and sample bottles needed for testing.
Corrective Action
The recommended treatment depends on the level and form of hydrogen sulfide and/or sulfate found in the water, as well as whether whole-house (point-of-entry) treatment or point-of-use treatment for drinking and cooking is needed. The best option will depend on how much hydrogen sulfide or sulfate is present in your drinking water. It is important to have your water tested by a certified laboratory to determine the concentration before purchasing any treatment system.
At higher levels, whole-house treatment is recommended. Lower levels can often be addressed with a point-of-use reverse osmosis system. Other options include using bottled water, especially for drinking and food preparation, or drilling a new well. If considering a new well, discuss with your well contractor whether a deeper or shallower well may be appropriate, and whether relocating the well on your property could help avoid the sulfur source.
If hydrogen sulfide is caused by sulfur bacteria in the plumbing system, chlorinating the well can help eliminate the bacteria. However, this is not always a permanent solution, as the bacteria may return. For more information on chlorination, see our guidance on Disinfection Procedure for Private Wells.
If the “rotten egg” odor is only present in hot water, it may be caused by a reaction involving the magnesium rod in the water heater. Replacing the magnesium rod with an aluminum or zinc rod may resolve the issue. If water temperatures are maintained above 150°F, only aluminum rods should be used. To be sure, consult a licensed plumber or heating professional.
Granulated Activated Carbon
If you have trace amounts (up to 0.3 milligrams per liter), installing an activated carbon filter will reduce the unpleasant taste, but it has limited capacity for odor absorption. For more information, see our guidance Granular Activated Carbon Treatment of Private Well Water.
Aeration
For levels below 2.0 milligrams per liter, aeration treatment can be effective. During aeration, oxygen reacts with hydrogen sulfide and converts it into an odorless, dissolved form of sulfate. After aeration, yellow sulfur particles may also form in the water.
One drawback of this method is that it can produce a strong hydrogen sulfide odor near the aeration unit, which may be unpleasant if the system is located near living spaces. For this reason, proper ventilation is required.
Aeration alone may not reduce hydrogen sulfide to undetectable levels. However, adding a granular activated carbon filter after the aeration system can help remove any remaining trace amounts. For more information, see our guidance on Granular Activated Carbon Treatment of Private Well Water and Aeration Treatment of Private Drinking Water Systems.
Iron Removal Filter
For levels between 1 and 10 milligrams per liter, an iron-removal filter containing manganese greensand may be used. Manganese dioxide oxidizes hydrogen sulfide particles that are then filtered out. The filters must be recharged with a potassium permanganate solution when the manganese greensand is depleted. If the pH of your water is below 6.7, a calcite neutralizer may need to be installed to increase the pH level, which will allow for better oxidation and filtration of the hydrogen sulfide. Refer to our guidance on pH – Acidity of Private Drinking Water Wells for more information.
Oxidizing Chemicals
Injection of an oxidizing chemical, such as chlorine or potassium permanganate, followed by a filter is the most common method for treating high concentrations of hydrogen sulfide levels at or above 6 mg/L. Sufficient storage must be provided to maintain 20 minutes of contact time between the water and the oxidizing chemical.
Chlorine treatment can be combined with a granulated activated carbon filter to remove the chlorine taste in the water. Yellow sulfur particles may cause a yellow film on clothing and fixtures. A sand or aggregate filter can remove the yellow particles. Backwashing the filter is necessary every few days or weeks to flush out the accumulated particles. Refer to our guidance on Granular Activated Carbon Treatment of Private Well Water and Microfiltration Treatment of Private Drinking Water Systems for more information.
Naturally Occurring Sulfates
When the problem is naturally occurring sulfate, small concentrations may be treated using point-of-use distillation and reverse osmosis systems. Large concentration may be treated using a whole-house ion exchange treatment system.
For more information on these treatment options see the following guidance:
• Distillation Treatment of Drinking Water Systems
• Ion Exchange Treatment of Private Drinking Water Systems
• Reverse Osmosis Treatment of Private Drinking Water Systems
