Hydrogen Sulfide-the Rotten Egg Smell in Well Water

Hydrogen Sulfide gas (H2S) gives water that awful “rotten egg” taste and smell and can be a fairly common occurrence in parts of the country, like Prince William County, Virginia where the groundwater is naturally high in sulfate. This problem can be solved, but let’s back up and start at the beginning. You have to first have sulfate present to have hydrogen sulfide. The EPA guidance for sulfate is 250 ppm for taste, but may be unnoticeable at higher levels, but excessive levels may have a laxative effect. Hydrogen sulfide naturally occurs in shale, sandstone, and near coal or oil fields, but can also be created by sulfur reducing bacteria “eating” the sulfate. According to the EPA, sulfur-reducing bacteria pose no known health risks. Sulfur-reducing bacteria live in oxygen-deficient environments such as deep wells, plumbing systems, water softeners, and water heaters. Often these bacteria flourish in plumbing systems. Sulfate reduction can occur over a wide range of pH, pressure, temperature, and salinity conditions and produce the rotten egg smell and the blackening of water and sediment by the formation of iron sulfide if iron is also present in the groundwater or plumbing system.  

Hydrogen Sulfide gas (H2S) with its characteristic “rotten egg” taste and smell can actually be detected as an off smell at 0.5 parts per million (ppm) by most people. At less than 1 ppm, hydrogen sulfide will give water a musty odor. At 1 to 2 ppm, it will have an odor similar to rotten eggs. Levels encountered in private wells are usually less than 10 ppm, because high levels of gas will not remain in solution in the water. Though toxic and potentially lethal at 800 parts per million after 5 minutes of exposure, the Occupation Safety and Health Administration, OSHA, OSHA has established 10 ppm (20 times the concentration that you can smell it at) as the safe limit. Hydrogen sulfide is heavier than air and can accumulate in pits and basements and can potentially create a health and explosive hazard (though the smell might kill you first). Hydrogen sulfide can be corrosive to metals such as iron, steel, copper, and brass, and it can cause yellow or black stains on kitchen and bathroom fixtures, but the big problem is the smell, the water is undrinkable and unusable with that smell. Some water treatment systems can actually create the problem within the plumbing system, and some water treatment companies that specialize in selling water softener systems for all problems may think that the problem is unsolvable, but that is not true. Most hydrogen sulfide problems can be solved if the correct solution is implemented. So if you smell Hydrogen sulfide in your well water you need to figure out what is going on to correctly identify a solution.

 Hydrogen sulfide can end up in your tap water by four different routes. (1) It can occur naturally in groundwater especially in oil rich shale and coal seams. (2) It can be produced within the well or plumbing systems by sulfur reducing bacteria (bacteria that essentially eat sulfate in areas that have a high natural level of sulfate in the rocks. It is only guessed at how the bacteria enter the well or plumbing system and how associated these bacteria are to the iron and manganese eating bacteria, but these anaerobic bacteria occur naturally in decaying plant material and soil and many areas in the nation have high natural levels of sulfate in the groundwater. (3) Hydrogen sulfide can form in hot water heater by either supplying a pleasant environment for the sulfate reducing bacteria to thrive or the energy for the magnesium rod intended to prevent corrosion of the heating tank to react with the sulfate naturally occurring in the water.  (4) Finally, there are instances where the hydrogen sulfide gas is due to contamination of the well with septic waste.

Because hydrogen sulfate is so easily smelled by the typical human being, just this one time, most (but not all) of the testing will be done by smell. You need to be systematic and frequently step outside the home so that you do not grow accustomed to the smell. First thing is to determine if the smell is coming from the plumbing system or the well system. You will need to smell the water coming out of the hot water faucet and cold water faucet. This is best done at a sink that has a so called widespread or centerset two handled faucet to ensure there is no mixing. Now run the hot water and smell. Note whether there is a hydrogen sulfide smell from that tap. Is the smell constant or does it diminish after the water has run a while, or is the smell variable. Now do the same for the cold water tap. After you finish this go outside and run the hoses and determine if there is hydrogen sulfide smell to that water and whether it diminishes or stays constant. Repeat the process to make sure that you get the same results.

If the smell is only from the hot water faucet and not from the cold water or the hoses, then the problem is in the hot water heater. It is either sulfate reacting with the magnesium anode rod, or sulfur reducing bacteria (flourishing) in the hot water tank.  Unless you are very familiar with operations and maintenance of hot water heaters, you should call a plumber. There is no standard test for sulfur reducing bacteria, so it is difficult to differentiate between a bacteria problem and something that might be solely sulfate reacting with the magnesium. You need to treat the hot water tank for both situations so it is a good idea to chlorine shock the hot water heater to kill the bacteria then flush it. But first start by raising the temperature in the hot water heater to 160 degrees Fahrenheit for three hours. This will generally kill the sulfur reducing bacteria. At this point you might want to flush the hot water heater a couple of times and let it heat back up and see if the problem is gone. This probably won’t last, if iron bacteria are being introduced from the well, but keeping your hot water heater at 160 degrees will constantly kill the bacteria. If you do not want to keep your hot water heater set so high, then move on to disinfecting the hot water heater and replacing the anode rod.

Either turn off the hot water heater if it is electric or put it on pilot if it is gas and drain off a few gallons of water after you close the cold-water inlet valve. Make sure that you have drained off a gallon or so and pour a half gallon of household bleach (5.25% hypochlorite) into the tank. Use either the temperature and pressure valve, anode rod opening, or hot water outlet pipe opening to pour the chlorine into the hot water heater. Let the chlorine sit in the tank for at least two hours. Then open the cold-water inlet valve, drain the hot water heater and turn the heat back up. If the problem is sulfate reacting with the magnesium anode (corrosion protection rod), it can be replaced with an aluminum rod that is not as reactive as the magnesium and may still serve to protect the metal components of the tank from corrosion. Most hot water tanks take a standard size anode rod and there are aluminum replacements available from several manufacturers. Generally, you should check the condition of the anode rod when you pour the bleach into the tank. Be aware that some high end tanks have two anode rods and replacing just one with aluminum will not solve the problem because the remaining magnesium rod will continue to react with the sulfate.  

If the hydrogen sulfide smell is in both the hot water facet and the cold water faucet, but not from the hoses, then the problem is likely to be sulfur reducing bacteria in the plumbing system (after the pressure tank). Sulfur reducing bacteria just love to live in water softeners. If there is a water softener in the house, first consider removing it. Water softeners are often installed as an expensive fix for a mild iron and manganese problem. High concentrations of dissolved hydrogen sulfide 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 (the hoses), it usually indicates the presence of some form of sulfate-reducing bacteria in the system. Water softeners provide an environment for these bacteria to grow. These “salt-loving” bacteria, that use sulfates as an energy source, may produce a black slime inside water softeners. If you have modest sulfate, but no rotten egg smell, installing a water softening system may create additional problems, especially if the system is not meticulously maintained. The first solution is to get rid of the water softener. Test your water to see how hard it actually is. If your water softener was really intended to solve an iron and/or manganese problem then it could be replaced with an oxidizing greensand filter which can be used to remove iron (with water with pH above 6.7) manganese and hydrogen sulfide. If your water is so hard that you cannot live with it, then you will have to disinfect the water softener (according to manufacturer recommendations or the instructions available from Minnesota Extension) and meticulously maintain and disinfect the water softener in the future.

If the hydrogen sulfide smell is strong when the water in either faucet is first turned on and then seems to go away after the water has run a while, then it is probably sulfur reducing bacteria in the well system or plumbing system. If the hoses do not have any hydrogen sulfide smell than the bacteria is in your plumbing system otherwise the bacteria is in the well or both the well and the plumbing system. When the hydrogen sulfide smell and taste problem is caused by the presence of sulfate and sulfur-reducing bacteria in the well or plumbing system then shock chlorination using a high dose of chlorine and sufficient contact time to kill the non-pathogenic iron, manganese and sulfur reducing bacteria which can be difficult to kill because of the associated slimy secretion. Effective treatment requires sufficient chlorine strength and time in contact with the bacteria. Though you typically use a chlorine concentration of 200 parts per million for decontamination of a well, a higher concentration is recommended for sulfur (and iron) reducing bacteria. Recommended concentrations are between 400-1,000 parts per million. Be warned that high concentrations of chlorine may affect water conditioning equipment, appliances such as dishwashers, and septic systems. You may want to check with the manufacturer of the appliances before chlorinating and be careful to drain as little as possible to the septic system. If you do not want to treat your well yourself, hire a well driller to disinfect the well. Be sure to tell them that you need about 4 times the usual amount of chlorine and do not need confirmation testing. (Typically well drillers do this for coliform bacterial contamination.) If you want to do this yourself, I like the instructions from either Minnesota or Virginia. Detailed instructions to calculate the amount of chlorine bleach to use and the steps to take to treat the well are available from either state, but Minnesota includes instructions for water softeners and other water treatment systems).Remember to use 4 times the chlorine they suggest for the initial well treatment since these are the instruction for the less persistent coliform bacteria.  

If the hydrogen sulfide smell is strong in the hoses and the hot and cold water faucets and remains fairly constant with use, then the problem is probably hydrogen sulfide gas in the groundwater.  As mentioned above, the oxidizing greensand filter can be a very effective solution for water that has both iron and manganese, or iron and hydrogen sulfide odor, or iron reducing or sulfur reducing bacteria. The pH of the water needs to be close to neutral (above 6.7-7) for a greensand filter to work, so now would be a good time to test the well water for iron, manganese, hydrogen sulfide, and coliform and E. coli bacteria. It is important to understand the quantities of hydrogen sulfide and to make sure that the well has not been contaminated with sewage waste. For higher levels of hydrogen sulfide injecting an oxidizing agent, like chlorine,before the pressure tank followed by an activated carbon filter can solve both a hydrogen sulfide problem and an iron problem. Generally, these systems should be installed by professionals and confirmation testing performed.