Water that is giving off a distinctive smell is most likely contaminated with hydrogen sulfide. Hydrogen sulfide does not usually pose immediate health problems at the levels it is found in domestic drinking supplies. However, it is certainly an inconvenience — especially to one’s nose, as it creates a “rotten egg” smell.
Hydrogen sulfide crops up in other ways too. The magnesium rod used in water heaters for corrosion control can chemically reduce sulfates to hydrogen sulfide, and sewage pollution can be a source. Hydrogen sulfide also can enter surface water through springs.
To test for hydrogen sulfide, contact a certified drinking water laboratory. Visit http://water.epa.gov/scitech/drinkingwater/labcert/statecertification.cfm for state-specific information on certified drinking water testing labs. The certification officer in your state can provide a list of certified labs in your area.
Hydrogen sulfide escapes (volatizes) from water easily, so samples should be tested on-site or immediately stabilized for laboratory analysis. Laboratory instructions should be followed very carefully.
If you do have a hydrogen sulfide level in your water that is higher than you would like, there are water treatment technologies available to address the problem.
- Activated carbon filters can be effective when hydrogen sulfide is present in low levels (up to about 0.3 ppm). The hydrogen sulfide is absorbed onto the surface of the carbon particles. Filters require periodic replacement and can harbor sulfate-reducing bacteria.
- Shock chlorination may reduce the hydrogen sulfide-producing bacteria. It’s most effective in water with a pH between 5 and 7 and ineffective in alkaline (higher pH) water. Contact time depends on concentration of chlorine in the water, water temperature, and pH. An activated carbon filter may be necessary to remove residual chlorine or small amounts of remaining hydrogen sulfide.
- Ion exchange resin absorbs hydrogen sulfide until the resin is exhausted, then the resin is regenerated with a salt. Suspended solids and precipitated iron can clog the unit and may require pretreatment.
- Manganese greensand filtration used to remove iron and manganese can also be effective with concentrations of hydrogen sulfide less than 5 ppm. These systems are specialized and require frequent maintenance.
- Oxidation removes hydrogen sulfide concentrations exceeding 6 ppm. It can be done by aeration, chlorination, and potassium permanganate.
- Oxidizing filters will work for concentrations up to 6 ppm. The filter contains sand with a manganese dioxide coating that changes hydrogen sulfide gas to tiny particles of sulfur that are trapped inside the filter.
- Ozone treatment creates a chemical reaction that precipitates sulfur. Ozone is effective for concentrations up to 10 ppm.
- Water heater modification is necessary when hydrogen sulfide is causing an odor within the water heating system. Replacing the magnesium corrosion control rod with one made of aluminum or other metals usually improves the situation. However, such action could void the manufacturer’s warranty on the water heater.