Causes

• Hydrogen sulfate occurs naturally in some groundwater supplies; it's also produced by sulfate-reducing bacteria, which get the energy they need through reactions that release hydrogen sulfide as a waste product. These sulfate-reducing bacteria can colonize environments like deep wells, plumbing systems and water heaters and taint the water with hydrogen sulfide. Water heaters equipped with a magnesium corrosion-control rod can sometimes sustain a reaction that produces hydrogen sulfide as well. In the worst-case scenario, sulfur water can be caused if the drinking water supply has become contaminated by sewage, in which case it may pose a serious threat to human health; this problem, however, is quite uncommon.
  
  

Testing

• If you suspect your drinking water is tainted with hydrogen sulfide, you may want to have it tested at an environmental laboratory; the cost is typically less than $50. Labs can also test a water sample for sulfate and sulfur bacteria as well. The rotten-egg odor is fairly unmistakable, so you can actually analyze the cause yourself with a simple sniff test. Your sense of smell will quickly become inured to the strong odor of hydrogen sulfide, so it's best to conduct this test after you've been out and have just returned home.
  
  

Concentrations

• If you do have a water sample tested by a lab, the lab will give you the concentration of the gas detected in the sample. Most people can smell hydrogen sulfide at concentrations as low as .5 parts per million (ppm). If the concentration exceeds 1 ppm, the water becomes more corrosive to plumbing. Concentrations of over 10 ppm are rare and should be dealt with immediately.
  
  

Finding the Source

• To determine the source, turn on both the hot and cold water faucets and check for the rotten egg odor. The scent will always be stronger around the hot water faucet, but if it's present only at the hot water faucet, the hot water heater is the most likely culprit. If the scent is present at both faucets but running the water causes the scent to diminish over time, you may have sulfate-reducing bacteria in the well or the water distribution system. If the scent is strong and persists without diminishing, the groundwater may contain hydrogen sulfide. Finally, if you have a water softener and the problem only occurs in water treated by the softener, you probably have sulfate-reducing bacteria in your water softener.
  
  

Treatment Options

• Once you've analyzed the problem, you have several different options for treatment. If the water heater is the culprit, you should contact a plumber to help you with the problem; he can disinfect the water heater with chlorine bleach or replace the magnesium anode with a zinc or aluminum anode (if the anode is the problem). Shock chlorination with a strong chlorine solution can treat a contaminated well or distribution system, although this job may be best left to a professional as well. Water softeners can also be disinfected in the manner specified in the manufacturer's instructions. If you have hydrogen sulfide gas in your groundwater, you can have a filter or an aerator to remove the gas from your supply.