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The Safe Drinking Water Act (SDWA), as amended in 1996, requires that EPA establish a program to monitor specified unregulated contaminants every five years. EPA published the first Unregulated Contaminant Monitoring Rule (UCMR 1) in the Federal Register on September 17, 1999 (64 FR 50556), the second (UCMR 2) on January 4, 2007 (72 FR 368), the third (UCMR 3) on May 2, 2012 (77 FR 26072), and the fourth (UCMR4) on December 20, 2016 (81 FR 92666). This action addresses SDWA requirements by establishing the terms for the fifth cycle of monitoring including a list of the new unregulated contaminants to be monitored during the UCMR 5 period of 2022 to 2026 (with sample collection expected to take place between 2023-2025). The proposed rule, published on March 11, 2021, fulfilled a key commitment in 'EPA's 2019 Per- and Polyfluoroalkyl Substances (PFAS) Action Plan' by proposing the collection of more drinking water occurrence data for a broader group of 29 PFAS.