Drinking Water FAQs:
Harmful Algal Blooms

Toxins from harmful algal blooms (HABs) can enter drinking water supplies from surface water sources or ground water sources supplied 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 cyanobacteria or cyanotoxins through my drinking water?

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

How do water treatment plants deal with cyanobacteria?

Because of the cost and complexity of existing analytical methods, municipal drinking water treatment plants with surface water supplies do not regularly monitor for algal toxins. They do use treatment techniques that would 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 porous media such as sand and charcoal. Disinfectants are also applied to inactivate pathogenic microorganisms.

Can I treat my water at home to remove cyanobacteria and their toxins?

People who are not on public water supplies should not drink surface water during an algal bloom even if it is treated, because in-home treatments such as boiling, disinfecting water with chlorine, or water filtration units do not protect people from cyanotoxins.

Can I cook using water with cyanobacteria in it?

Even if cyanobacteria are present in the watershed, they are effectively removed by your drinking water provider through treatment. You should not expect to have algal toxins in your tap water.  If your water does not come from a public water system and you are notified of an algal bloom or observe algae, you should not use the water for cooking. Boiling water does not remove cyanotoxins. Because it is impossible to detect the presence of toxins in water by taste, odor or appearance, you are better off assuming they may be present.

What about using water with cyanobacteria for washing?

If cyanobacteria are visible, try to find a better source of water for washing food, dishes, and clothes. Also avoid bathing or showering in water containing cyanobacteria, as skin contact with cyanobacteria may lead to skin irritation or other adverse health effects.

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).

Cyanotoxins on the
Drinking Water Contaminant Candidate List (CCL)

Cyanotoxin Number of known variants or analogues Primary organ affected Health effects Most common cyanobacteria producing toxin
Microcystin-LR 80~90 Liver Abdominal pain

  • Vomiting and diarrhea
  • Liver inflammation and hemorrhage
  • Acute pneumonia
  • Acute dermatitis
  • Kidney damage
  • Potential tumor growth promotion
Microcystis
Anabaena
Planktothrix
Anabaenopsis
Aphanizomenon
Cylindrospermopsin 3 Liver Abdominal pain

  • Vomiting and diarrhea
  • Liver inflammation and hemorrhage
  • Acute pneumonia
  • Acute dermatitis
  • Kidney damage
  • Potential tumor growth promotion
Cylindrospermopsis
Aphanizomenon
Anabaena
Lyngbya
Rhaphidiopsis
Umezakia
Anatoxin-a group 2-6 Nervous system Tingling, burning, numbness, drowsiness, incoherent speech, salivation, respiratory paralysis leading to death Anabaena
Planktothrix
Aphanizomenon
Cylindrospermopsis
Oscillatoria

In June 2015, the EPA issued Drinking Water Health Advisories (HAs) for microcystins and cylindrospermopsin following extensive research into their health effects in drinking water. EPA found there are adequate health effects data to develop HAs for microcystins and cylindrospermopsin, but found the data inadequate to develop an HA 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.

References and More Information