The “rotten egg” smell emitted by some water is caused by high levels of hydrogen sulfide in the water. According to experts at the Ohio State University Extension Service,Hydrogen sulfide is formed by sulfur bacteria that may occur naturally in water. These bacteria use the sulfur in decaying plants, rocks, or soil as their food or energy source and as a by-product produce hydrogen sulfide. The sulfur bacteria do not cause disease, but their presence in water can cause a bad taste or odor.
Water heaters can also be sources of foul odors stemming from hydrogen sulfide. A magnesium rod is often placed in the tank by the manufacturer to prevent water heater corrosion. Sulfur that is dissolved in water can react with the magnesium rod forming hydrogen sulfide. The magnesium rod can be replaced with an aluminum one or removed completely. Removal however, may void the company's warranty.
But if your tap water smells like rotten eggs and tastes a little funny, is it unhealthy? Probably not. You can’t really tell about water quality from water odor, its look, or even taste. It’s the “silent” contaminants, the ones that don’t trigger your senses, that you need to worry about: lead from pipes in old houses; arsenic that naturally occurs in the earth; or microorganisms, pesticides and fertilizers that wash away from farms and lawns into storm drains and wind up in our drinking water supplies. All of these have been linked to serious illnesses.
Experts agree that the U.S. has one of the safest drinking waters supplies in the world, but that is no guarantee. For the best assurance of safety, you should periodically test your water through an independent, certified lab. Labs offer a variety of testing packages (lead, minerals, volatile organic chemicals, radon, bacteria, pesticides) at a range of prices ($30-$250).
There are also home test kits for various contaminants that may cause water odor. To find a lab, check your local yellow pages, get suggestions from your health department, call EPA's Drinking Water Hotline (1-800-426-4791), or visit www.epa.gov/safewater/.