For many Marietta and Cobb County residents, turning on the tap lately has come with a surprise: water that smells or tastes a bit like damp earth. While this can be alarming, the good news is straightforward. The water remains safe to drink. The unusual flavor is linked to a naturally occurring compound called MIB, and the regional water provider is actively working on it.
What Is MIB & Why It Matters to the Nose, Not the Doctor
The current issue centers on 2-Methylisoborneol, better known as MIB. It is a naturally occurring substance produced by certain algae and bacteria that live in lakes and reservoirs. MIB often appears alongside another compound called geosmin.
Both MIB and geosmin:
- Affect taste and odor, not safety
- Are typically described as earthy or “lake-like”
- Can be noticed by some people at extremely low levels
For context, taste and odor concerns usually begin around 10 nanograms per liter, or 10 parts per trillion. Some people with very sharp senses can pick it up at levels above about 5 parts per trillion. That is roughly equal to about half a cent in a billion dollars, which explains why it is hard for treatment plants to remove and very easy for human noses to detect.
Health agencies and drinking water professionals do not consider MIB and geosmin a public health risk at the levels found in drinking water. The issue is aesthetic, not medical, although it can certainly make a glass of tap water less appealing than normal.
Why It Is Happening Now
Seasonal changes are a big part of the story. As warmer weather shifts to cooler conditions and reservoir levels change, algae and bacteria in lakes can produce more MIB and geosmin. In this case, the Cobb County-Marietta Water Authority (CCMWA) has recorded record MIB levels in the Chattahoochee River, which supplies the Quarles Drinking Water Treatment Plant in east Cobb…