Back to WIC Info Page
Water for Our Future

IISG-98-15 Water Taste and Odor
L. E. Dorworth, Department of Biological Sciences, Purdue University Calumet, Hammond, Indiana

Have you ever noticed a musty smell and or an earthy flavor in your water? For the communities located along the Lake Michigan shoreline, this has become a seasonal experience. This is nothing new. Taste and odor problems go back in history to the impoundment of surface water for uses.

For the city of Chicago, first reports of noticeable drinking water problems relating to taste and smell were brought to the attention of the City of Chicago Water Department in the summer of 1994. Since then, the taste and smell of the water has been a complaint of water customers particularly in the late summer/early fall. The problem is seasonal typically beginning in the spring and in again the fall at the time lake water turns over. The lake water temperature tends to be in the 60ºF range at the time of the algal bloom.

Why is this occurring and how is the problem being treated?

Although these problems have been occurring since long before zebra mussels were ever introduced to the Lake, one hypothesis is that the zebra mussels, due to their filtering activities, have made the water clearer, enabling light to penetrate to a deeper depth in the water column. The deeper penetration of light through the water enables various algal populations to persist. The maximum depth in Lake Michigan for algal growth as well as zebra mussel activity is 30 feet. The most suitable substrate for zebra mussel colonization is the shallow, rocky reefs found along the coast.

The earthy, musty taste and smell of the drinking water is related to two naturally occurring compounds, geosmin and 2-methylisoborneol. Research shows two commonly encountered microorganisms, actinomycetes (bacteria) and cyanophytes (bluegreen algae) produce these compounds as metabolic by-products. An increase in these organisms will have a consequential increase in the taste and odor complaints.

The problem results from a build-up during the warm summer months of blue-green algae which contains a naturally occurring compound called geosmin. In the past, the algal problem has been of short duration and is usually dispersed by a sudden drop in water temperature resulting in replacement of surface water. It can last longer if the weather is particularly dry and sunny.

Another factor, which may increase the taste and odor problem, is the enhanced growth of the algae. Due to deeper light penetration, the benthic algae Zygnemapalean has grown prolifically in the lake. This algal species requires high light, which it is getting due to the zebra mussel filtering activity. As the summer progresses, the algal community productivity increases until late summer early fall at which time it begins to die. The algae, which is filamentous loses a foothold on the substrate and begins to wash up along the coast.

In nature, the natural process is decomposition. Fungal and bacterial communities decompose the algae in the water. The decomposers are hydrophillic (water lovers) and are common in natural water systems. The response of the decomposers is to increase in numbers as the algal communities begin to die off. Their increased growth is due to an increase in available substrate.

Typically, water treatment for taste and odor problems from Gary, Indiana, to Waukegan, Illinois, has been the increased use of Powdered Activated Carbon (PAC). Presently, PAC used at the Chicago Water Treatment plants is approximately 60 to 80 pounds per 1,000,000 gallons of water. The other method for treating the water is through the use of Granulated Activated Carbon (GAC). Approximately twenty inches of the GAC is added to the top of seven rapid sand filters. The activated carbon in PAC and GAC removes organic carbon from the water supply. In order to do this, maximum contact time between the water and the carbon is necessary. On a summer day, the Chicago water treatment facility may process 900 million gallons of water a day while maintaining adequate contact time between the carbon and the water. The main advantage of PAC compared to GAC is that the powdered form concentrations can be controlled to match the need for taste and odor control. It is expected that the powdered form would be used to mitigate short duration taste and odor problems.

Ecosystem Response to the Zebra Mussel Infestation

Interactions between native aquatic species have been dramatically altered due to the mussel infestation. In fact, new ecosystems have been created, which tend to be unstable blooms (bluegreen algae) have occurred in Saginaw Bay in 1994 and 1995. Similar blooms have occurred in western Lake Erie in 1995. The link between bluegreen algae and drinking water taste and odor has been documented. The relationship between the bluegreen algae and the zebra mussels feeding on the algae may result in enhancing the bluegreen algal growth. When the bluegreen algae enter the zebra mussel siphon, they are coated with a mucous and are periodically expelled as undigested pseudofeces from the mussels. In most cases, the bluegreen algae are returned to their environment as viable cells. Other features which may be considered beneficial or not a beneficial contribution to the water by the zebra mussel communities are: improvements in water clarity; a change in the zone of primary productivity from the pelagic to the pelagic/benthic zone; a significant increase in the benthic algal biomass an productivity (mainly the filamentous green algae); an increase in the benthic nutrient concentrations; increase in the submerged plant distributions and productivity; an increase in the abundance and diversity of benthic invertebrates; and increased bacterial (actinomycetes) abundance.

The influence of the zebra mussel on the drinking water supplies at this point is only theoretical. However, the magnitude of changes must be taken into consideration when treating water supplies for the populations located around the Great Lakes.

Recommended Resources
Using filtration and induced infiltration intakes to exclude organisms from water supply systems. Engineering Notes. 1992. P.Keilor. 13p -a literature review plus an overview of slow sand filtration and infiltration systems.

Acknowledgements
The following individuals provided insight and help on this topic: Don Jensen from the Highland Park Water District, Highland Park Illinois; Ellen Flannigan at the Chicago Water Treatment Facility; Nancy Tuchman at Loyola University Chicago; and the Indiana Department of Environmental Management.