Metro Atlanta residents have been complaining about tap water that suddenly smells and tastes earthy or musty this fall, and water officials say they know exactly why: Lake Lanier, the main drinking water source for the region, is going through its annual autumn turnover, stirring up natural compounds and affecting systems that draw from the lake.
As reported by The Georgia Sun, algae and bacteria living in lake sediment produce two compounds, geosmin and 2-methylisoborneol, or MIB, that cause the earthy or musty smell and taste showing up in faucets this season. During summer, Lake Lanier separates into a warm upper layer and a cold lower layer, but as autumn cooling sets in, surface water gets colder and heavier and sinks, mixing the lake’s bottom layers in a process known as turnover. That mixing stirs up the geosmin and MIB that settled into the sediment, and this fall, concentrations of both compounds are running higher than usual, according to the same report.
In a February 2026 episode, following resident complaints the previous week, the Gwinnett County Department of Water Resources adjusted its treatment processes, including its ozonation system, which led to a significant drop in taste and odor calls, per 11Alive. Gwinnett County’s water-treatment system includes the Lanier and Shoal Creek Filter Plants, and the department serves nearly one million residents. County officials said their treatment typically handles taste and odor issues when compound levels are low, but some smell or taste may linger when geosmin and MIB peak, even though the water continues to meet all state and federal drinking water standards.
Why the Smell Is So Noticeable at Such Tiny Concentrations
The reason so many people are noticing something is off comes down to how sensitive the human nose actually is. According to Paragon Laboratories, the human nose can detect geosmin and MIB at concentrations near 5 to 10 parts per trillion, levels so minute that standard gas chromatography-mass spectrometry lab testing can be used to detect them. Federal regulators draw a clear line between that kind of aesthetic nuisance and an actual health hazard. The U.S. Environmental Protection Agency describes secondary drinking-water standards as non-enforceable guidelines for aesthetic effects such as taste and odor, distinct from primary standards that govern actual health risks…