Drain odors are a common problem in many homes and are typically noticed when running the water in a sink, shower or bathtub. Initially it seems that the water stinks, but a little detective work and proper knowledge will help you discover and eliminate the source of the odor.

To determine where the smell is coming from, plug the drain before running the water, so your nose is not already filled with the odor. Now turn the water on. If you don't detect the smell, then the culprit is probably a combination of rotting, mildewing dirt and hair debris lodged in the P-shaped trap under the fixture and a buildup of a bacteria-filled slime layer (biofilm) on the sides of the vertical drain pipe. As water rushes past the slime and debris, odor-causing molecules dislodge and drift up out of the drain into your nose.

To eliminate the odor's source, remove the strainer cover from the shower drain or the stopper mechanism from the sink drain so you can see into the drainpipe. Use soap and water and a larger-diameter bottlebrush to thoroughly clean the underside of the strainer, the stopper mechanism, the drain assembly and the sides of the vertical drainpipe, then rinse thoroughly with hot water. In addition, pour a solution of one or two parts household bleach to 10 parts water into the drain and let sit overnight to kill the odor-causing bacteria. The bleach solution is also helpful if the drain cover or stopper mechanism cannot be removed.

If you don't like using chemicals, have a septic system, or are cleaning a garbage disposal drain that can be damaged by bleach, consider this natural drain cleaner. Pour 1/2 cup of baking soda into the drain followed by 1/2 cup of white vinegar. The baking soda is basic and the vinegar is acidic, so they will react with a churning action that will help clean the drain.

Also, if a sink or shower is used infrequently, the water in the P-trap below the drain can evaporate allowing sewer gasses to come up through the drain into your home. To prevent this from happening, make sure the trap never dries out by periodically running water in the sink or shower. 

Does your hot water smell?

Even though the City of Mesa chlorinates every water source before it enters the distribution system, sulfur or "rotten-egg" odors can develop in water heaters. Incidences of these odors in hot water are primarily due to the presence of sulfates and their reaction with sulfate-reducing bacteria that can thrive in the conditions provided by a water heater. The odors may occur due to one or a combination of the following factors: setting the water heater temperature too low and/or inactivity during vacations when the water sits for days, weeks or months.

Despite the offensive odor, the presence of sulfates at levels detected in the City of Mesa's drinking water and the sulfate-reducing bacteria living in the water heater are not harmful to your health. This simple test will help you determine whether the odor is coming from the hot or cold water:

Cover the drain (odors commonly occur in the drain pipe) and run the hot water. Note if you detect the rotten-egg odor. Next, move to another faucet in the house, cover the drain and run the cold water. If the cold water has an odor, please contact the City of Mesa Water Quality Services for further assistance. If you determine that the odor is only in the hot water, then it is most likely originating in the water heater.

The remedy may be as simple as killing the bacteria with increased heat. Sulfate-reducing bacteria die at about 140 degrees Fahrenheit. Water heaters are factory set at 140 degrees, which is the medium setting on the temperature control dial. Increasing the temperature to the high setting - 160 degrees Fahrenheit - for several hours should kill the sulfate-reducing bacteria. It is just as important to then flush the water heater to remove the dead bacteria. The fastest way to do this is by turning on the hot water in the bathtub for 10 to 15 minutes. CAUTION: The hot water tank must have an operable pressure relief valve; otherwise this method of treatment may be dangerous. The temperature setting must be reduced following treatment to prevent scalding hot water and to avoid high energy costs.

For more information about Drain Odors
Please contact the Water Quality division at (480) 644-6461.