filling water bottle


Cylindrospermopsin is a cyanotoxin produced by certain species of cyanobacteria (formerly referred to as blue-green algae). Cyanobacteria are sometimes found in surface water when conditions favor growth and formation of algal blooms.

People can be exposed to cylindrospermopsin by:

  • ingesting fish or shellfish from waters containing cylindrospermopsin;
  • having direct skin contact with water containing cylindrospermopsin through showering, swimming or wading;
  • breathing airborne cylindrospermopsin while boating, waterskiing or recreating in waters with cylindrospermopsin present; or
  • consuming drinking water containing cylindrospermopsin.
Drinking water treatment generally removes intact cyanobacterial cells and low levels of cyanotoxins from source waters, but during a severe algal bloom, some cylindrospermopsin may escape treatment.


Short-term exposure of humans to drinking water contaminated with cylindrospermopsin can produce symptoms such as fever, headache, vomiting, diarrhea, enlarged liver and kidney damage with the loss of water, electrolytes and protein. No reliable data on humans are available on the exposure levels of cylindrospermopsin that induced these effects.
The best way to know if cylindrospermopsin is a concern in your source water or treated drinking water is to contact your water utility or state public health agency. Depending on the source of your water, climate and potential for nutrient pollution, your utility may or may not monitor for cylindrospermopsin and other cyanotoxins. Some sources are more likely to be at risk from cylindrospermopsin than others. For example, if your water comes from groundwater sources, it’s not likely to contain cylindrospermopsin.

Cylindrospermopsin in drinking water is not currently regulated by the U.S. Environmental Protection Agency. Several states have guidelines for utilities for monitoring and addressing cylindrospermopsin and other cyanotoxins in drinking water. You can contact your water utility to determine how cyanotoxins are addressed in your state.

In 2015, EPA issued a drinking water health advisory for cylindrospermopsin. Health advisories are non-regulatory levels to assist public health professionals. No negative health impacts are anticipated at these concentrations. EPA has provided two different ten-day health advisory levels – 0.7 microgram/liter for bottle-fed infants and young children and 3.0 micrograms/liter for school-aged children and adults.

Regulators, utility managers and public health officials use health advisories to consider what management practices are necessary and if additional actions are necessary when cylindrospermopsin is found.

The Safe Drinking Water Act (SDWA) requires EPA to publish a list of substances that could potentially be of concern and warrant further study. This is known as the Contaminant Candidate List (CCL), and cylindrospermopsin is on the list.

Under the SDWA, EPA is also required once every five years to issue a new list of up to 30 unregulated contaminants to be monitored by public water systems. This is known as the Unregulated Contaminant Monitoring Rule. Cylindrospermopsin is included in the fourth round of UCMR (UCMR4). Testing for UCMR4 starts in January 2018 and will continue through December 2020. The data from this nationwide monitoring will inform and support EPA’s decisions on regulatory actions to protect public health.

Typically, groundwater wells are not expected to contain cyanotoxins such as cylindrospermopsin. However, if your well is affected by surface water it could also contain cylindrospermopsin.

If your well is influenced by surface water, then you should take additional steps to address potential contaminants. EPA has information available on their private drinking water well page. Your local health department is another reliable source of information regarding steps you should consider.

If you are concerned about cylindrospermopsin in your drinking water, you may consider purchasing a home treatment device. However, there is limited information on the effectiveness of at-home treatment devices on removing cylindrospermopsin from drinking water. There are some organizations currently developing certification standards to test residential treatment devices to evaluate how well they remove cylindrospermopsin and other cyanotoxins from drinking water. These standards are expected to be published soon. To make a well-informed and cost-effective decision, consider:

If you decide to use a home treatment device, be sure to follow manufacturer instructions for proper care and maintenance of the device.

Bottled water in the United States is regulated by the U.S. Food and Drug Administration and is required to meet standards equal to EPA’s tap water standards. There are also individual state standards. In most cases, you must contact the bottled water manufacturer for information about cyanotoxin levels.