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Drinking Water FAQs: Harmful Algal Blooms

Toxins from harmful algal blooms (HABs), called cyanotoxins, can enter drinking water supplies from surface water sources or ground water sources impacted by surface water. An increase in the incidence of HABs around the country has prompted the Environmental Protection Agency (EPA) to issue guidelines and recommendations for cyanotoxin values in drinking water and recommendations for public water system operators to use in the management and treatment of certain cyanotoxins.

How likely is it that I could be exposed to cyanotoxins through my drinking water?

Customers receiving drinking water from public water systems are not expected to be exposed to cyanotoxins, as all public waterworks have to comply with stringent regulations pertaining to water treatment and monitoring.

How do I know if my water source might be impacted by HABs?

Surface water sources (e.g., reservoirs or lakes) may be impacted by HABs. Reach out to your drinking water provider for more details on precautions taken to keep customers safe from cyanotoxins. If you source your own water, you should monitor your intake water body for HABs and consider alternative sources if a bloom is observed. Water sourced from a well is not expected to be at risk from HABs.

How do water treatment plants deal with cyanotoxins?

Because of the cost and complexity of existing analytical methods, municipal drinking water treatment plants with surface water sources do not regularly monitor for cyanotoxins. They do however use treatment techniques that could remove the toxins if they were present.

Conventional water treatment facilities can remove the cells of algae and other growing organisms by adding chemicals that bind them together. As the cells clump together, they become heavier and fall to the bottom of settling basins. Additional removal is obtained by mandatory filtration through sand or charcoal. Disinfectants are also applied to inactivate pathogenic microorganisms.

Are there any guidelines to protect drinking water from cyanotoxins?

Currently, there are no U.S. federal water quality regulations for cyanotoxins in drinking water under the Safe Drinking Water Act (SDWA) or in recreational waters under the Clean Water Act (CWA). The EPA has listed microcystin-LR, cylindrospermopsin, and anatoxin–a on the Drinking Water Contaminant Candidate List (CCL).

In June 2015, the EPA issued Drinking Water Health Advisories for microcystins and cylindrospermopsin following extensive research into their health effects in drinking water. EPA found there are adequate health effects data to develop advisories for microcystins and cylindrospermopsin, but found the data inadequate to develop an advisory for anatoxin-a. The EPA also published recommendations for public water systems that include management strategies for testing and treating cyanotoxins in drinking water as well as guidance on when to issue “do not drink, do not boil” health advisories.

I have more questions

Visit the EPA’s Harmful Algal Blooms page for more helpful resources or contact the Utah Division of Drinking Water.

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