The City of Maryville is currently experiencing taste and odor issues in the water treatment process as a result of increased Geosmin levels in the raw water supply at Mozingo Lake. Geosmin is a naturally occurring compound produced by bacteria in soil and algae found in surface water. Cold temperatures kill off algae in surface water and dead algae then release geosmin. This compound can produce a musty, earthy smell and taste which can generally be detected by humans at low levels.
While the taste and odor can be unpleasant, geosmin is not toxic or harmful. The water remains safe to drink and on-going testing continues to show all water leaving the Maryville Water Treatment Plant exceeds minimum standards for drinking water established by the Missouri Department of Natural Resources (MDNR).
The general threshold for human detection is about 15 nanograms per liter, however, people with sensitive pallets can detect geosmin in the drinking water at concentrations as low as 5 nanograms per liter. This is why some customers notice the taste and odor while others do not. When geosmin or other algae related compounds are noticeable, customers are encouraged to chill the water in a refrigerator or add a few drops of lemon juice to improve the taste and reduce odors. On the contrary, heating the water increases the volatility of these compounds, which explains why the smell is more easily detected when you are in the shower or when used for hot beverages.
Adjustments in the water treatment process are being made and include adding Powdered Activated Carbon (PAC) to reduce the level of geosmin. PAC applications are able to obtain an 88-90% reduction in levels, however the remaining percentage is impossible to remove through the current technology at the water treatment plant. The treatment process is delicate and applying too much PAC
can foul treatment membranes, and other adjustments can cause high turbidity creating maximum contaminate level (MCL) violations.
On June 22, 2020, the City hired HDR Engineering, Inc. to complete a Water Treatment Alternatives Analysis to provide both short- and long-term recommendations for addressing taste and odor issues. A draft version of those recommendations is currently under review. Recommendations are expected to range from additional algicide applications at the lake to the construction of a new multi-million-dollar water treatment plant with updated technologies. A full report will be presented to the City Council later this month.
In addition, source water protection efforts continue in the Mozingo Lake Watershed to improve the quality of raw water. Partnerships with the Missouri Rural Water Association, Missouri Department of Natural Resources, Soil & Water Conservation District, and the USDA Natural Resources Conservation Service are underway to establish a variety of funding sources for improvements and implementation of best practices throughout the watershed.
Mozingo Lake provides a stable source of raw water for the Maryville community and beyond. However, it is an aging living ecosystem and algal blooms, including geosmin, are common in many jurisdictions across the United States and elsewhere in the world. Please note, that the City of Maryville remains committed to expediting the elimination of these taste and odor concerns while improving the public drinking water system for the long-term.