Health-Based Screening Levels (HBSLs) are non-enforceable water-quality benchmarks that can be used to (1) supplement U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) and Human Health Benchmarks for Pesticides (HHBPs), (2) determine whether contaminants found in surface-water or groundwater sources of drinking water may indicate a potential human-health concern, and (3) help prioritize monitoring efforts. HBSLs were developed by the U.S. Geological Survey (USGS), historically by the National Water-Quality Program (NWQP) for contaminants without USEPA MCLs or HHBPs.

HBSLs were updated in January 2024 (or April 2024, for PFAS chemicals) in order to:

• Update toxicity information and benchmarks for the 835 contaminants included in the online searchable HBSL database, including 10 contaminants with HBSLs added since the last (2018) update.
• Update all HBSLs to be consistent with new USEPA methods and exposure assumptions.
• Replace HBSLs for 4 contaminants that have new USEPA HHBPs.
• Add MCLs, proposed MCLs or develop HBSLs for 27 per- and perfluoroalkyl substance (PFAS) compounds, which are newly added to the HBSL database.

The searchable table below contains 835 contaminants, of which 192 have HBSLs, 93 have MCLs or proposed MCLs, 144 have HHBPs, and 406 have no available benchmark. MCLs and HHBPs are provided for user convenience; for more information about them, and to obtain current values, please visit the respective USEPA websites. Learn more about HBSLs and guidance on their use.

Glossary, Metadata, and Documentation

• Download Glossary and Metadata: Excel (.xlsx) file with an explanation of all acronyms used in the table and related metadata.
• Download Documentation for HBSLs: Excel (.xlsx) file with the detailed supporting toxicity information used to calculate HBSLs and related metadata.