During the warm-weather months, we occasionally experience some taste and odor problems with the water received from Lake Michigan via the Evanston Treatment Facility. In communication with them, they have assured us that the water is safe for usage and our local testing reaffirms this fact. The following explains the cause of this problem:
Communities which draw on Lake Michigan for their drinking water, and this amounts to the majority of the Chicagoland area and its suburbs, have been hearing complaints from residents that their water has an odd taste, which has been described variously as musty, moldy, or earthy. The musty taste is elusive and subtle. One family member will take a sip and make a face, but another will not be able to taste it. And it comes and goes. It may appear in Hammond or Chicago, where the Water Department got more than 150 calls about it during one weekend. Just as suddenly, it will go away. On a daily basis, it can shift from one plant to another.
The musty, moldy taste comes from at least two compounds which are produced by the decaying of dead algae, the tiny drifting plants which are found in every body of water. Decaying algae and other micro-organisms give off a variety of organic chemical compounds, any or all of which could make water taste moldy.
None of those decay products has been found to pose a health threat, especially at the low concentrations found in open bodies of water. They may not be dangerous, but they are powerful in the effect they produce. Sensitive palates make it difficult to eliminate the taste completely for everyone, but there is a straight-forward way to treat raw lake water to get rid of most of the taste.
Finely ground particles of carbon are added to water as soon as it arrives in the plant. Carbon attracts molecules which adhere to it like steel to a magnet. The carbon settles out of the water later in the treatment process. The only problem is that carbon is not cheap. It costs about 50 cents per pound.
A seasonal problem with earthy water is nothing new. In the late fall, as the temperatures drop, the top layer of the lake cools first. Cold water is denser than warm water so it drops to the bottom and the warmer layers rise in its place. The process, called the fall turnover, stirs up sediment and brings up decaying alagae. But for at least the last three years, the water has had an odd taste in the summer, too. With conditions in the lake changing unpredictably, the art behind removing the musty taste lies in matching the dosage of carbon with the magnitude of the problem.
Please be assured that your water may taste a bit odd, but it is safe to drink. If you have any questions or concerns, please contact the Department of Public Works at (847) 705-5200.