Kitchen sink with a tall faucet, dishes, fruit, and cleaning supplies on the counter — A kitchen sink and countertop sit ready for everyday use in a home kitchen. Forsyth County residents who notice an earthy taste in tap water are being urged to check with their water provider for the latest notices.

An earthy taste in a glass of water can begin miles away, in Lake Lanier.

Forsyth County draws its raw water from the lake, where naturally occurring organisms can produce compounds that leave a musty smell or taste. In a September 14 notice, the county pointed residents to two familiar culprits: geosmin and methylisoborneol, usually shortened to MIB.

What causes the taste?

Certain algae and bacteria naturally produce these compounds. Their production can increase in late summer and early fall, particularly when water is warm and lake levels are low.

People can notice remarkably small amounts. The Cobb County-Marietta Water Authority’s explanation of geosmin and MIB says taste and odor commonly become noticeable around 10 parts per trillion, with some people detecting even lower concentrations.

That helps explain why a change can seem strong at the kitchen tap even when the amount of the compound is tiny.

Does an earthy smell mean the water is unsafe?

Geosmin and MIB are taste-and-odor compounds. The U.S. Geological Survey identifies them as nuisance substances rather than harmful chemicals. Forsyth County’s September notice likewise said the compounds are not toxic or harmful.

That finding applies to those compounds. An unfamiliar smell alone cannot establish what is in a particular glass of water, and a seasonal explanation does not replace a utility’s current advisory.

Why can the taste remain after treatment?

Removing odor compounds can require treatment beyond the processes normally used to produce drinking water.

The Cobb County-Marietta Water Authority, for example, uses activated carbon to reduce geosmin and MIB. Its treatment information illustrates why water can meet drinking-water requirements while still having an unwelcome taste. It does not describe Forsyth County’s specific treatment setup.

What can residents do?

First, check the provider named on the water bill and look for its latest notices. A Cumming mailing address does not necessarily mean the household is served by Forsyth County Water and Sewer.

If the provider has confirmed a seasonal taste-and-odor issue, chilling water or adding lemon can make it more pleasant, according to the Cobb County-Marietta Water Authority. Those steps improve taste; they do not treat contamination.

Report a sudden or persistent change to the utility, including when it began and whether it affects every tap. Follow any instructions the provider issues for the affected service area.