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Monitoring Unregulated Drinking Water Contaminants

Occurrence Data for the Unregulated Contaminant Monitoring Rule

EPA uses the Unregulated Contaminant Monitoring Rule (UCMR) to collect data for contaminants suspected to be present in drinking water, but that do not have regulatory standards set under the Safe Drinking Water Act (SDWA). The monitoring provides 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.

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UCMR 4 (2018-2020) Occurrence Data

UCMR 4 was published in the Federal Register on December 20, 2016. It requires monitoring for 30 chemical contaminants (nine cyanotoxins and one cyanotoxin group; two metals; nine pesticides; three brominated haloacetic acid [HAA] disinfection byproducts groups, three alcohols, and three semivolatile organic chemicals). This dataset is not complete. Data are added and possibly removed or updated over the course of this reporting cycle following further review by the analytical laboratories, the public water systems, the states and EPA.

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UCMR 3 (2013-2015) Occurrence Data

UCMR 3 was published in the Federal Register on May 2, 2012. It required monitoring for 30 contaminants: 28 chemicals and two viruses.

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UCMR 2 (2008-2010) Occurrence Data

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

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UCMR 1 (2001-2005) Occurrence Data

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

Caution should be used in any interpretation of the subject data, since this table contains all data reported for UCMR 1, including untreated source water data from several states. Any positive result from untreated source waters, which are subsequently treated, are generally not used to conduct exposure assessments. Rather, such cases generally triggered finished water sampling at the entry point to the distribution system.

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

The Unregulated Contaminant Monitoring-State (UCM-State) Round 1 dataset contains public water system (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(52 MB)  
    Data fields included in the Rounds 1 & 2 database table:
    • PWSID (Pubic 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 Pivot Tables.
  • Rounds 1 & 2 MS Excel PivotTables ®(762 K)  
    Data included in Rounds 1 & 2 pivot table:
    • 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 Pivot Tables 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.

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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 data sets were assembled into a single "national cross-section" data set that is indicative of contaminant occurrence nationally.

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

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