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.
In November 2025, the Chattahoochee reached a record MIB concentration of 137 parts per trillion. By comparison, the highest level recorded in 2024 was 19 parts per trillion. All drinking water utilities that pull from Lake Lanier or the Chattahoochee River are facing similar taste and odor challenges this season.
MIB is notoriously difficult to treat. Standard water treatment processes do not remove it very well, which is why utilities turn to advanced options such as powdered activated carbon. Even then, MIB can linger at levels that sensitive customers still notice.
Where Cobb’s Drinking Water Comes From
The Cobb County-Marietta Water Authority is a wholesale water provider that supplies drinking water to more than 900,000 residents. It is separate from Cobb County Government and the City of Marietta, even though those local governments are among its customers.
A few key facts about CCMWA:
- It is unique because it draws water from two separate river basins.
- It operates two large treatment plants:
- Quarles Treatment Division in East Cobb, supplied by the Chattahoochee River.
- Wyckoff Treatment Division in northwest Cobb, supplied by Lake Allatoona.
- Each plant has a treatment capacity of 86 million gallons per day, for a total system capacity of 172 million gallons per day, making CCMWA the second largest wholesale water provider in Georgia.
Wholesale customers include:
- Cobb County Water System
- City of Marietta
- City of Smyrna
- Paulding County Water System
- City of Austell
- City of Woodstock
- City of Mountain Park
- Lockheed Martin Corporation
- Douglasville/Douglas County Water & Sewerage Authority
So if the water tastes or smells odd in one part of Cobb County, and perfectly normal in another, that usually reflects which plant is supplying that area at the moment.
What CCMWA Is Doing To Address Taste and Odor
CCMWA’s Simmons Laboratory routinely monitors MIB and geosmin at both treatment plants and at seven sampling sites on Lake Allatoona. Testing frequency increases from late spring through late fall, when these compounds are more likely to rise.
In the current situation, CCMWA has taken several steps:
- Shifting production toward Wyckoff
The Wyckoff plant, which uses Lake Allatoona as its source, is not seeing elevated MIB levels. CCMWA has shifted more production to Wyckoff to reduce the number of customers receiving water from the Quarles plant. - Maximizing powdered activated carbon (PAC)
At the Quarles plant, operators are applying powdered activated carbon at the maximum design capacity to help reduce the taste and odor issues. Reducing the plant’s flow rate helps improve PAC contact time and performance. - Using granular activated carbon (GAC) at Wyckoff
At the Wyckoff facility, part of the treated water receives additional polishing through a granular activated carbon facility before entering the distribution system. This step helps remove taste and odor compounds when they are present. - Planning for future upgrades
CCMWA has committed funding and staffing to evaluate advanced treatment processes in 2026 to improve taste and odor control over the long term.
Meanwhile, MIB levels are monitored daily, and operations are adjusted as conditions change. Through all of this, CCMWA reports no health concern associated with the current MIB levels. The water remains safe to drink.
What Residents Can Do At Home
Although the water is safe, no one dreams of ordering “earth-flavored” water with dinner. Residents who notice an unpleasant taste or smell have several practical options that can help the situation in the glass, even while work continues at the plant.
Helpful at-home steps include:
- Use an activated carbon filter
Pitcher filters such as Brita or Pur, faucet-mounted filters, and many refrigerator filters use activated carbon, which can reduce MIB levels and improve taste. - Chill the water
Cold water tends to mute taste and odor. Filling a pitcher and keeping it in the refrigerator can make the flavor far more acceptable. - Try the fridge dispenser
For homes with a refrigerator water dispenser, pulling water from that line can help, since it typically passes through a carbon filter first. - Add a bit of lemon
Adding lemon juice before chilling can further improve flavor. A small splash can go a long way toward masking earthy notes.
For residents who have ever said, “Water does not have a flavor,” this season is making quite a counterargument. Fortunately, most people find that filters plus cold temperatures bring things back into familiar territory.
Who To Call With Questions
Customers with lingering concerns about taste and odor, or questions about testing and treatment, can reach CCMWA directly at (770) 514-5300 or contact their local water service provider, such as Cobb County Water System at (770) 419-6200 or Marietta Power & Water at (770) 794-5150.
While the current MIB spike is unusual, it fits a known pattern tied to algae activity, weather, and reservoir conditions. Utilities across the region are seeing the same seasonal spike and are responding with a mix of treatment strategies and longer term planning.
Until natural conditions improve and treatment adjustments catch up, the best approach at the household level is to filter, chill, add a little lemon, and remember that the odd flavor is a nuisance, not a health threat.
