Maximum contaminant level

Maximum contaminant levels (MCLs) are standards that are set by the United States Environmental Protection Agency (EPA) for drinking water quality.

The MCL for a contaminant may be higher than the MCLG because of difficulties in measuring small quantities of a contaminant, a lack of available treatment technologies, or if EPA determines that the costs of treatment would outweigh the public health benefits of a lower MCL.

In the last case, EPA is permitted to choose an MCL that balances the cost of treatment with the public health benefits.

Since these contaminants do not cause health problems, there are no legally enforceable limits on their presence in drinking water.

[8] In some cases, a state may issue an MCL for a contaminant that has not been regulated by EPA under federal law.