DDW Proposes Microplastics Definition

This morning the State Water Resources Control Board (SWRCB) Division of Drinking Water (DDW) posted for public comment a proposed definition of microplastics in drinking water (Microplastics_DDW Proposed Definition).  Also enclosed is the DDW staff report describing the research and process to develop the definition. (DDW Staff Report_Microplastics)

DDW’s Proposed Definition of Microplastics

‘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.

[Note: DDW’s proposed definition includes two footnotes that expand on the text.  See the enclosed document.]

Next Steps

  1. The SWRCB will hold a workshop on the definition of ‘Microplastics in Drinking Water’ on April 8, 2020 at 9:30 a.m., available via webcast (https://video.calepa.ca.gov/).
  2. Written comments are due by 12:00 noon on Friday, April 24, 2020.
  3. A resolution to adopt the proposed definition will be on the agenda for the SWRCB Meeting on Tuesday, June 16, 2020 at 9:30 a.m.  Also available via webcast (https://video.calepa.ca.gov/).


Senate Bill 1422 was signed into law in 2018 (adding section 116376 to California’s Health and Safety Code).  This new law requires the following activities from DDW:

  1. On or before July 1, 2020: adopt a definition of microplastics in drinking water;
  2. On or before July 1, 2021:
    1. Adopt a standard methodology for testing of microplastics in drinking water;
    2. Adopt requirements for four years of testing and reporting of microplastics in drinking water, including public disclosure of those results;
    3. Consider issuing quantitative guidelines (e.g., notification level) to aid consumer interpretations of the testing results, if appropriate; and
    4. Accredit qualified laboratories in California to analyze for microplastics in drinking water.