Geosmin and MIB (2-methylisoborneol) are natural-occurring terpene compounds (volatile unsaturated hydrocarbons found in plant essential oils). These two specific terpene compounds cause taste and odor problems in drinking water even at extremely low concentrations. People have described the taste and odor as earthy or musty. There are more than 40 different species of cyanobacteria that can produce geosmin or MIB, along with multiple soil-dwelling bacteria. Like cyanotoxins, they are released into the water when the cyanobacterial cell dies (lyse).

The most important message when it comes to geosmin and MIB is that they are not toxic at levels found in nature. While not toxic, they have been described as revolting, nauseating, and disgusting. People will commonly call their water supplier to complain, and it can be difficult to convince customers that the water is safe to drink.



If there is treatment in the source water itself, such as using copper sulfate in the water body, and the cells lyse, then one option is suspending use of the water intake until the compounds can move past the intake, then the system can avoid pulling in the less desirable raw water. 

If unable to avoid the dissolved geosmin or MIB, another potential option for pretreatment would be activated carbon. While activated carbon has proven to be highly effective, natural organic matter (NOM) needs to be monitored carefully. If NOM levels are high, more activated carbon may be necessary. If low, carbon levels would need to be adjusted to avoid unnecessary costs. A sedimentation step to remove the carbon from the water would also be necessary.

Coagulation, flocculation, and sedimentation can be highly effective in removing intact cyanobacterial cells. It is important to carefully monitor pH during this time. If the pH is allowed to drop below 5, as could happen during the addition of coagulant, it can cause the cells to lyse. If the system recycles their supernatant, this practice should be suspended as it would introduce these compounds back into the treatment stream.

Rapid filtration can help capture any remaining cells in the sand layer while the carbon layer can adsorb dissolved compounds. Slow filtration can capture intact cells while the compounds are degraded by the colonized bacteria. One consideration to keep in mind, is that it is possible for some organisms that create taste and odor problems to colonize the filters. If taste and odor problems are evident after filtration, this may have occurred.

Common disinfectants such as free chlorine, chlorine dioxide, chloramines, and potassium permanganate have shown to not be effective in treating geosmin and MIB. Ozone, ultraviolet (UV), and hydrogen peroxide treatments have shown positive results, but the use of hydrogen peroxide may require another treatment step to “quench” or “use up” the remainder of the unused solution.

There is evidence that nanofiltration membranes could remove a high percentage of geosmin and MIB.

Water Treatment for Purification from Cyanobacteria and Cyanotoxins provided the majority of information for this newsletter. 

• Online tools to help create a HAB response plan for your public water system

• The Idaho Department of Environmental Quality will be hosting a free virtual Drinking Water Operator training on December 15, 2022. The course is being submitted for 0.6 CEU approval. Register for the event at DEQ's Surface Water Treatment Optimization for Harmful Algal Blooms – Free Online Training page.

• Real-Time Risk Characterization Tool for Harmful Algal Blooms – EPA Water Research Webinar Series (November 16, 2022).

• Dealing with Cyanobacteria: Time to Make a Plan – Washington State Department of Health Guidance for Developing a Harmful Algal Bloom Management and Response Plan.

• A Water Utility Manager’s Guide to Cyanotoxins – AWWA and the Water Research Foundation.

• Toxic Cyanobacteria in Water – World Health Organization (Downloadable).

• Previous Idaho Drinking Water HAB Newsletters can be found at the Idaho DEQ website page: Cyanobacteria Harmful Algal Blooms.