Of all the contaminants found in drinking water, one frequently occurring (in terms of violations) is chlorate.

Basic Information

 What is chlorate?

There are many forms of chlorate, so this question isn’t always easy to answer, so we are following the guidance of the World Health Organization documentation. Generally speaking chlorate is a negatively charged ion (an anion) that is in the process of cleaning and disinfecting water (as is chlorite). Other chlorate compounds (like sodium chlorite, and chlorine dioxide) are also found in drinking water and can get in through other means, such as the bleaching of paper or through fertilizer run off. These are often grouped under the general term “chlorate”.

Perchlorate (ClO4) may be grouped alongside chlorates or tracked separately. This compound occurs naturally, often in dry regions, so it is a concern in the southwestern region of the United States, but it can also appear in drinking water in manufactured forms, such as perchloric acid and the salt ammonium perchlorate. Manufactured perchlorate is most often used as an oxidizing agent in propellants (like fireworks, airbags, and signal flares).

Chlorate in Drinking Water

Chlorate (Oxyhalide Anion) is tracked by the EPA via the Unregulated Contaminant Monitoring Rule 3. As the name suggests, it is part of a list of chemicals that is not regulated but is known to be unhealthy above certain levels so the EPA delivers a guidance to water suppliers, so it is tracked by the UCMR to see if there is a wider health concern. The Health Reference Level (HRL) for chlorate in US drinking water is 210 µg/L.

Chlorate has known healthy effects that include (given sufficient doses) causing problems with the nervous system in infants and causing anemia. This is true of fetuses in pregnant women as well. It can also be absorbed by the human thyroid, as can perchlorate. (Reference)