Geosmin (pronounced "jee-OZ-min") is a naturally occurring compound produced by a number of microorganisms found in soil and aquatic environments, including surface water. When these microorganisms die, they release geosmin.

Geosmin events typically last a short duration and can occur intermittently when raw water sources turn over (e.g. water at the bottom of a lake rises to the top) or when source water temperatures in lakes or canals are high. Drought conditions that produce low flows from source waters along with high temperatures can also allow the microorganisms that produce the geosmin to thrive.

Geosmin typically produces an earthy or musty odor and/or taste. The ability to detect the smell or taste of geosmin varies by individual. The general threshold for human detection is about 15 parts per trillion (ppt). However, some people are naturally more sensitive to geosmin and can detect it when the concentration is as low as 5 ppt. For reference, 1 ppt is equivalent to one droplet of water in an Olympic-sized swimming pool.

Geosmin can and does occur in a variety of areas served by the City of Santa Clara, mainly south of Homestead Road.

While the taste and odor can be unpleasant to some people, geosmin is not toxic or harmful, nor is it regulated by the EPA. The water continues to meet State and local drinking water standards. For more information about water quality in the City of Santa Clara and how it is tested, you can download our annual Consumer Confidence Report.

While it is difficult to determine the exact duration that geosmin is present in the water supply, geosmin events are more common during months of high heat. So, as the weather cools down, the amount of geosmin should naturally decrease.

To improve the taste of water, regular household filtration will assist with reducing the smell and/or flavor of geosmin in your drinking water. You can try chilling it, adding ice cubes, a slice of lemon, or a few drops of lemon juice. Heating the water increases the volatility of the compounds in geosmin, which explains why the odor is more easily detected when you are showering or using water for hot beverages or cooking. 

Geosmin is common in surface water around the world. Some water treatment plants make no attempt to remove the compound due to the cost involved and the fact that geosmin is not harmful.