On March 19, 2020, the State Water Resource Control Board for the U.S. state of California announced the publication of a draft definition of “microplastics in drinking water,” accompanied by a staff working document with additional specifications. The proposed text includes the following:

“Microplastics in Drinking Water are defined as solid polymeric materials to which chemical additives or other substances may have been added, which are particles which have at least two dimensions that are greater than 1 and less than 5,000 micrometers (μm). Polymers that are derived in nature that have not been chemically modified (other than by hydrolysis) are excluded.”

The agency notes that evidence related to the hazards and exposures to microplastics is rapidly evolving and that there is a current lack of standardized methods for detecting microplastics. Therefore, it makes clear that this proposed definition could be changed in the future in response to new information. An email communication from the agency announced that the draft definition is currently open for public comment until April 24, 2020. A meeting is planned at the California Environmental Protection Agency on June 16, 2020 to consider adopting the proposed definition.

The agency is legally bound to adopt a definition by July 1, 2020, and by July 1, 2021 it is required to: (i) adopt a standard methodology for testing microplastics in drinking water, (ii) adopt requirements for four years’ worth of testing and reporting of microplastics in drinking water, (iii) consider issuing quantitative guidelines, and (iv) accredit qualified laboratories in California to analyze microplastics in drinking water.

Read more

California Water Boards (March 20, 2020). “Microplastics.”


California Water Boards (March 9, 2020). “Proposed Definition of Microplastics in Drinking Water.” (pdf)