Occurrence Data from the Unregulated Contaminant Monitoring Rule

The EPA uses the Unregulated Contaminant Monitoring Rule (UCMR) to collect data for contaminants that are suspected to be present in drinking water and do not have regulatory standards set under the Safe Drinking Water Act (SDWA). The monitoring provides the EPA and other interested parties with nationally representative data on the occurrence of contaminants in drinking water, the number of people potentially being exposed, and an estimate of the levels of that exposure. These data can support future regulatory determinations and other actions to protect public health.

To improve accessibility and transparency of the UCMR occurrence data, the EPA standardized the data fields across the UCMR datasets and developed two tools: the UCMR 5 Data Finder and the UCMR Archival Data Finder. These tools allow people to easily search for analytical results from each UCMR cycle. Selected results can be downloaded as a Microsoft Excel file (downloads are limited to one million records). For those interested in large-scale data processing using statistical or data analysis software, the EPA recommends using the associated UCMR occurrence data text files provided on this page (standardized in March 2024) which contain the analytical results for each cycle as well as additional information reported during monitoring, if applicable.

Before conducting your own assessment of the data, please review the Instructions for Accessing UCMR Results and the Data Summary documents on this page.

Instructions for Accessing UCMR Results (pdf) (345.48 KB)

On this page:

UCMR 5 Data Finder

UCMR 5 was published in the Federal Register on December 27, 2021. It requires monitoring for 29 per- and polyfluoroalkyl substances (PFAS) and lithium with sample collection from January 2023 through December 2025. The data released to date represent approximately 55% of the total results that the EPA expects to receive. Occurrence data will be updated on a quarterly basis until completion of data reporting in 2026. Data are added and possibly removed or updated over the course of this reporting cycle following further review by analytical laboratories, public water systems (PWSs), states, and the EPA. 

The UCMR 5 Data Finder includes the analytical results to date from UCMR 5 monitoring. Results can be filtered using multiple data fields, including PWS ID or name, PWS size, state, contaminant, source water type, results at or above UCMR minimum reporting levels (MRLs), and results above health-based reference concentrations.

UCMR 5 (2023-2025) Occurrence Data

UCMR Archival Data Finder

The UCMR Archival Data Finder includes the analytical results from past UCMR monitoring. Results can be filtered using multiple data fields, including UCMR cycle, PWS ID or name, PWS size, state, contaminant, source water type, and results at or above UCMR minimum reporting levels (MRLs).

UCMR 4 (2018-2020) Occurrence Data

UCMR 4 was published in the Federal Register on December 20, 2016. It required monitoring for 30 chemical contaminants.

The UCMR 4 occurrence data were revised in March 2024 to reflect minor corrections to the analytical result records for three samples; a total of 25 duplicate records were removed and one additional record was added to the UCMR 4 dataset.

UCMR 3 (2013-2015) Occurrence Data

UCMR 3 was published in the Federal Register on May 2, 2012. It required monitoring for 30 contaminants.

UCMR 2 (2008-2010) Occurrence Data

UCMR 2 was published in the Federal Register on January 4, 2007. It required monitoring for 25 contaminants.

UCMR 1 (2001-2005) Occurrence Data

UCMR 1 was published in the Federal Register on September 17, 1999. It required monitoring for 26 contaminants.

The UCMR 1 occurrence data were revised in March 2024 to reflect the addition of small PWS monitoring results for 1,3-dichloropropene. The EPA tasked the laboratories contracted to analyze small PWS samples with reporting results for this additional unregulated contaminant since it was within the scope of the methods already performed for the UCMR 1 contaminants.

Caution should be used in any interpretation of the UCMR 1 data, since some untreated (i.e., raw) source water data from several states are also included in the results. Any positive result from untreated source waters, which are subsequently treated, is generally not used to conduct drinking water exposure assessments. Rather, such cases generally triggered finished water sampling at the entry point to the distribution system.

UCM-State Rounds 1 and 2 (1988-1997) Occurrence Data

The Unregulated Contaminant Monitoring-State (UCM-State) Round 1 dataset contains PWS monitoring results for 62 then-unregulated contaminants (some have since been regulated). These data were collected by 40 states and primacy entities between 1988 and 1992.

The Round 2 dataset contains PWS monitoring results for 48 then-unregulated contaminants. These data were collected by 35 states and primacy entities between 1993 and 1997.

  • Rounds 1 & 2 database in MS Access (zip) (49.68 MB)  
    Data fields included in the Rounds 1 & 2 database table:
    • PWSID (Public Water System Identification Code)
    • EPA region
    • State
    • In national cross-section?
    • Water system type
    • Size category (based on people served by the system)
      • 1 = Very Small <=500
      • 2 = Small 501-3,300
      • 3 = Medium 3,301-10,000
      • 4 = Large 10,001-100,000
      • 5 = Very large >100,000
    • Population served by the system
    • Source_type
    • Contaminant Code
    • Contaminant Name
    • Detect?
    • NonDetect?
    • Result (for detects)
    • Sample collection date
    • Round (sample collected in Round 1 or Round 2)
    Details on these attributes are provided in the PivotTables.
     
  • Rounds 1 & 2 MS Excel PivotTables ® (zip) (744.45 KB)  
    Data included in Rounds 1 & 2 PivotTable:
    • This PivotTable contains information on Rounds 1 & 2 sample data. Any or all of the following facts for a contaminant-
      • # analyses performed
      • # PWS with analyses
      • # detects
      • # PWS with detects
      • minimum detect
      • maximum detect
      • mean detect
    • can be categorized by any combination of the following water system attributes:
      • EPA Region
      • State
      • Water system type
      • Size category *
    • or any combination of the following sample attributes:
      • Which Round the sample is from *
      • Whether the data was included in the national cross-section (which is a function of the state and the Round)
      • Sample collection year *
      • Source water type where the sample was taken *
      * To avoid double-counting, the PivotTables will not sum the number of PWSs with and without detects across this dimension or attribute. Details on these attributes are provided in the PivotTables.

UCM Data Summary Reports

The summary report (June 2001) includes summary descriptions of the contaminants from the Round 1 and Round 2 datasets, data quality assessments, and contaminant occurrence analyses. Also included is a description of how individual state datasets were assembled into a single "national cross-section" dataset that is indicative of contaminant occurrence nationally.

The complete national occurrence report (May 2001) provides full descriptions and details.

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Last updated on October 28, 2024