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The EPA uses the Unregulated Contaminant Monitoring Rule (UCMR) to gather information for contaminants that are suspected to be present in drinking water and do not have health-based standards set under the Safe Drinking Water Act. These data can support future regulatory determinations (i.e., the process that addresses potential regulatory actions for unregulated contaminants) and other actions to protect public health.

UCMR 5 requires monitoring by certain public water systems (PWSs) for 29 per- and polyfluoroalkyl substances (PFAS) and lithium in drinking water between 2023 and 2025. All community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) serving more than 10,000 people, all those serving between 3,300 and 10,000 people (subject to availability of appropriations and sufficient laboratory capacity), and a representative sample of those serving fewer than 3,300 are required to monitor during a single 12-month timeframe in the three years of monitoring. Please visit here for more details.