Homeowners often have more tolerance for water hardness and staining than for unpleasant water odors. If you are on a municipal water supply, your biggest complaint is probably the unpleasant odor of chlorine (not to mention its taste and the potential for the presence of harmful chlorine byproducts). Potential health issues related to chlorine are far more impactful than other aesthetic considerations. The rationale for chlorine use (and for its removal by homeowners) has been covered in previous columns, which are available on our website (www.goodwatercompany.com).

The second most common complaint regarding municipal water is the so-called "rotten egg" smell commonly attributed to hydrogen sulfide gas resultant from bacterial activity. This type of bacterial contamination itself does not necessarily indicate the existence of a health hazard but rather is more annoying than harmful. Most water bacterial testing is directed toward identifying the presence of pathogenic organisms. A sample may test negative for coliform bacteria and E. coli yet contain annoying aesthetic contaminants.

Sulfur or "rotten-egg" odors can develop in water heaters and in corroded iron piping, even if the water supply is chlorinated city water and the amount of sulfate is minor. Increased bacterial growth depletes both the oxygen and the chlorine residual in the piping. This can also occur if the water circulation has been inactive for some time. It is a common complaint in second homes and vacation homes. The unpleasant smell is created by nonpathogenic, sulfate-reducing bacteria that produce enzymes and accelerate the reduction process. Diagnosis is simple because this smell is more common on the hot-water side.

A water heater can provide an ideal breeding ground for the conversion of sulfate to hydrogen sulfide gas by creating a warm environment where sulfur bacteria can thrive, and by sustaining a reaction between sulfate in the water and the water heater anode rod. You can kill the bacteria by raising the water heater temperature to about 160 degrees Fahrenheit (provided you have a pressure relief valve); but you should also consider shock-chlorinating and draining the water heater. Another (controversial) solution is to remove or replace the sacrificial anode rod.

If there is an odor in the cold water, and the source is chlorinated city water, investigate the composition of the pipe. Odors can develop even in cold-water piping in the home, especially in galvanized iron piping, which can become corroded, providing a good environment for bacteria to grow and odors to develop. As a first step to eliminating bacterial odors, one might also chlorinate the piping, flush it, and see if the bacterial odors can be eliminated.

The EPA's Secondary Standards are nonenforceable guidelines that include recommendations for contaminants that may impact taste, color, and odor. These effects, which are much more complicated on well water, are not considered to present a risk to human health when measured under these standards. To learn the source of odors in your water, and how to eliminate the odors, seek out testing by qualified professionals.



Stephen Wiman has a background in earth science (Ph.D. in geology) and is the owner of Good Water Company in Santa Fe. He may be reached at 505-471-9036 and skwiman@goodwatercompany.com.