Tap water in Johns Creek is safe to drink, Fulton County says, despite a musty or earthy taste some residents have noticed.

Fulton County Public Works posted a notice on its water quality webpage confirming it has received reports of a noticeable taste and odor from customers north of the Chattahoochee River. The county's north Fulton service area includes Johns Creek, Alpharetta, Roswell, Milton and other communities.

The culprits are two naturally occurring compounds called 2-Methylisoborneol (MIB) and geosmin. Cyanobacteria, commonly known as blue-green algae, produce MIB and geosmin in warm surface waters, especially in late summer and early fall. The compounds enter the water supply through seasonal turnover in the Lake Lanier-Chattahoochee River system, which feeds the Atlanta-Fulton County raw water reservoir.

The compounds do not pose a health risk, according to the county's notice, which states the water "continues to meet our high safety standards."

The Tom Lowe Atlanta-Fulton County Water Treatment Plant, located in Johns Creek, is adding activated carbon to the treatment process to reduce the taste and odor. County operations crews are also flushing the distribution system to clear affected water. The process may take a few weeks, the county said.

The issue is regional. Forsyth County posted a notice on Monday, Sept. 14 reporting elevated MIB levels in its own water supply drawn from Lake Lanier. Based on Sept. 1 sample results, the raw-water MIB concentration entering Forsyth County's treatment facility measured approximately 213 parts per trillion. Forsyth County said levels have been elevated for an extended period compared with prior years, and that the issue affects "many other local counties and utility providers" that draw from Lake Lanier.

The seasonal taste-and-odor cycle is a recurring event for north Fulton County customers. In October 2025, Fulton County Public Works Director David Clark said in a county news release that the department was "committed to transparency" and wanted "to assure all residents that their water is of the highest quality."

Residents with questions about the taste or odor can call Fulton County at 404-612-9426.