Fifth Unregulated Contaminant Monitoring Rule

The Safe Drinking Water Act (SDWA) requires that once every five years the EPA issue a list of unregulated contaminants to be monitored by public water systems (PWSs).

The fifth Unregulated Contaminant Monitoring Rule (UCMR 5) was published on December 27, 2021. UCMR 5 required sample collection for 30 chemical contaminants (29 per- and polyfluoroalkyl substances [PFAS] and lithium) between 2023 and 2025. This monitoring provides a basis for future actions to protect public health.

• 40 CFR (Code of Federal Regulations, Title 40) Part 141: Final - Revisions to the Unregulated Contaminant Monitoring Rule (UCMR 5) for Public Water Systems and Announcement of Public Meetings (pdf) (27 pp, 650 K, About PDF)
• UCMR 5 Program Overview Fact Sheet (pdf) (281.64 KB, December 2021, EPA 815-F-21-009)
  • Hoja informativa del programa (pdf) (383.27 KB, December 2021, EPA 815-F-21-009S) (Spanish Version)
• Sample Collection Training Video for Small Public Water Systems
• EPA Approved Laboratories for UCMR 5

On this page:

• UCMR 5 Questions and Answers
• UCMR 5 Scope, Analytical Methods, and Contaminants

UCMR 5 Questions and Answers

The EPA released the final UCMR 5 dataset for 29 PFAS and lithium in August 2026.

The UCMR 5 dataset helps inform the EPA's PFAS OUT initiative to enhance engagement with PWSs and share resources, tools, funding, and free Real Water Technical Assistance (RealWaterTA) to help address PFAS in drinking water. The EPA's RealWaterTA initiatives work with PWSs nationwide to identify affordable solutions to assess and address PFAS. Services offered to PWSs include water quality testing, development or technical plans, operator training support, designing public engagement and outreach strategies, and support for accessing federal funding opportunities.

Answers to common questions are provided below.

1. Where can I access UCMR 5 results?
2. Where can I find a summary of health information about UCMR 5 contaminants?
3. Are public water systems (PWSs) required to report their UCMR results to their customers?
4. What concentration units are UCMR analytical results reported in?
5. What is a minimum reporting level (MRL) for the UCMR program?
6. How are UCMR 5 results for the NPDWR PFAS compared to the MCLs in the EPA’s Data Finder and Data Summary?
7. What should I consider before downloading the detailed UCMR 5 results?
8. How do I import the UCMR 5 data text files into Excel?
9. I don’t see UCMR 5 results for a particular PWS. Where are they?
10. How does the EPA ensure that the UCMR laboratory data are accurate?
11. What visualization tools are available to view PFAS occurrence data?
12. Where can I find more information about PFAS in drinking water?
13. What are the environmental sources and uses of lithium?
14. Why was lithium included in UCMR 5 and what information is available?
15. How can lithium be removed from drinking water?

1. Where can I access UCMR 5 results?

   The UCMR 5 analytical results are publicly available through the UCMR 5 Data Finder, the UCMR Occurrence Data webpage (via text files), and the PFAS Analytic Tools. The UCMR 5 Data Finder allows people to easily search for, summarize, and download the available UCMR 5 analytical results. Results can be filtered using multiple data fields, including public water system (PWS), PWS size, state, contaminant, source water type, results at or above UCMR minimum reporting levels (MRLs), and results above health-based drinking water reference concentrations. For those interested in large-scale data processing using statistical or data analysis software, the EPA recommends using the text files containing the UCMR 5 analytical results, as well as additional data element and ZIP Code information reported by participating PWSs. The UCMR 5 Data Summary summarizes the UCMR 5 results to date at the national level, available contaminant health effects information, and data considerations and definitions for the UCMR 5 Data Finder and text files. A document with instructions and tips for accessing results and a video demonstration of the UCMR 5 Data Finder are available on the UCMR Occurrence Data webpage.

2. Where can I find a summary of health information about UCMR 5 contaminants?

   The UCMR 5 Data Summary identifies previously published information and publicly available EPA resources that provide context around UCMR 5 results in relation to their minimum reporting levels (MRLs), legally enforceable regulatory levels (if applicable), and available non-regulatory health-based drinking water reference concentrations. Within the Data Summary, the regulatory levels for certain PFAS (i.e., maximum contaminant levels [MCLs]) and the available reference concentrations (i.e., health reference level [HRL] for lithium, USGS health-based screening levels [HBSLs] for certain PFAS) are provided in the same units as UCMR 5 results (µg/L); underlying final toxicity assessment values (e.g., EPA Integrated Risk Information System [IRIS]) are provided in mg/kg-day.

3. Are public water systems (PWSs) required to report their UCMR results to their customers?

   PWSs are required to notify customers through Tier 3 Public Notification (PN) about the availability of all UCMR results no later than 12 months after they are known by the PWS. Community water systems (CWSs) are also required to report UCMR results in their annual Consumer Confidence Report (CCR) when contaminants are found (i.e., measured at or above minimum reporting levels [MRLs]). CWSs must report the average and range of the prior year’s monitoring results. If timing and delivery requirements are met, CWSs may include their PN within their CCR, also known as an annual drinking water quality report, which is to be delivered to all billing customers each year by July 1. EPA resources for PWSs are available on the CCR and PN Compliance Help webpages. CCR and PN requirements need to be met for all UCMR 5 results (including results for the UCMR 5 PFAS that are now subject to the National Primary Drinking Water Regulation [NPDWR]) and are separate from the PFAS NPDWR CCR and PN requirements.
   
   For a copy of your local CCR, you may contact your local water supplier or use the EPA’s CCR search tool.

4. What concentration units are UCMR analytical results reported in?

   Analytical results from the UCMR program are reported by laboratories and provided by the EPA in micrograms/liter (µg/L, or parts per billion). To convert results in µg/L to nanograms/liter (ng/L, or parts per trillion), multiply the value by 1,000.

5. What is a minimum reporting level (MRL) for the UCMR program?

   The EPA established minimum reporting levels (MRLs) for lithium and the 29 PFAS included in UCMR 5. Only analytical results at or above the UCMR MRL are reported to the EPA. The EPA establishes MRLs to ensure consistency in the quality of the information reported to the agency. UCMR MRLs are determined using data from multiple laboratories that participate in EPA’s UCMR MRL-setting studies and are not associated with contaminant health effects information. The UCMR MRL is the lowest measurable concentration of a contaminant that, with 95% confidence, is achievable by at least 75% of laboratories nationwide using a specified analytical method (recognizing that individual laboratories may be able to measure or quantify analytes at lower levels). The EPA’s MRLs for the 29 PFAS included in UCMR 5 range from 0.002 to 0.02 µg/L (parts per billion), which is equivalent to 2 to 20 ng/L (parts per trillion). The practical quantitation levels (PQLs) for the NPDWR PFAS are based on the UCMR 5 MRLs; both represent quantitation levels. For more information about the PQLs, refer to the Federal Register Notice for the final PFAS NPDWR. The EPA’s MRL for lithium is 9 µg/L (parts per billion). For more information, please refer to the UCMR 5 Data Summary.

6. How are UCMR 5 results for the NPDWR PFAS compared to the MCLs in the EPA’s Data Finder and Data Summary? 

   On April 10, 2024, the EPA announced the final National Primary Drinking Water Regulation (NPDWR), including legally enforceable standards, or Maximum Contaminant Levels (MCLs), for certain PFAS monitored in UCMR 5. On May 18, 2026, the EPA announced two proposed rules related to PFAS in drinking water. The first rule proposes to uphold the NPDWR for PFOA and PFOS, while providing an option for PWSs to request two additional years to comply with the MCLs. The second rule proposes to rescind the regulations for PFHxS, PFNA, HFPO-DA (commonly known as GenX), and the Hazard Index mixture of these three PFAS plus PFBS. UCMR 5 results for the NPDWR PFAS do not indicate compliance or noncompliance with the MCLs. PWSs may work with their state to submit their UCMR 5 monitoring data to meet some or all of the PFAS NPDWR's initial monitoring requirements. Information provided on this page for UCMR 5 results is for technical assistance only and does not supersede the PFAS NPDWR requirements in 40 CFR 141 and 40 CFR 142. For more information, refer to the EPA's PFAS Final NPDWR and NPDWR Implementation websites.

   Compliance with the PFAS regulatory MCLs will be determined by calculating the running annual average (RAA) of quarterly results for each sample point, based on compliance monitoring data reported to the primacy agency. Recognizing that the UCMR 5 results have no direct implications for PWS MCL compliance, but that many are interested in comparing UCMR 5 data to the MCLs, the EPA calculated annual averages for the UCMR 5 results where such a calculation was possible. The agency then compared those averages to the NPDWR MCLs. Please note: the UCMR 5 averages for sampling locations with ground water sources are based on two results, not four.

   The UCMR 5 Data Finder and Data Summary each provide a table with the number of sampling location averages and PWSs with averages to date that are greater than the MCLs for NPDWR PFAS. The UCMR 5 Data Finder also provides a filterable table of the UCMR 5 averages for sampling locations in comparison to the MCLs. For UCMR 5 monitoring, PWSs may have multiple sampling locations, for which there are either two or four sample events over a period of 12 months (for locations with ground water or surface water sources, respectively). Sampling locations were only considered in the comparison to each MCL if they had a corresponding full set of UCMR 5 results (i.e., two or four results). 

   The MCLs for PFOA and PFOS are expressed with two significant digits; MCLs for HFPO-DA, PFHxS, PFNA, and the HI are expressed with one significant digit. Comparison of UCMR 5 averages to MCLs is based on the corresponding number of significant digits. For example, averages ≥0.00405 µg/L for PFOS or PFOA, and ≥0.015 µg/L for HFPO-DA, PFHxS, or PFNA, round to 0.0041 µg/L and 0.02 µg/L, respectively, and are identified as above the MCLs. Similarly, averages ≥1.5 for the Hazard Index (HI) round to 2 are identified as above the MCL if at least two of the four PFAS included in the HI are measured at or above the UCMR 5 MRL.

7. What should I consider before downloading the detailed UCMR 5 results?

   There are multiple options for viewing the UCMR 5 results. The UCMR 5 Data Finder allows people to quickly search for and summarize available UCMR 5 results by multiple data fields, including PWS, name or ID, PWS size, state, EPA Region, contaminant, source water type, results at or above UCMR minimum reporting levels (MRLs), and results above health-based reference concentrations. This tool is available to federal, state, and local agencies as well as others to easily locate and retrieve specific results and assist with answering questions regarding UCMR 5 monitoring. Selected results can be viewed online or downloaded as an Excel file (.xlsx) (downloads are limited to one million records).

   Monitoring results are also provided in tab delimited occurrence data text files (.txt). The data in these text files can be imported into various data analysis and software programs. The text files have field names in the first row and no text qualifier. The EPA recommends importing all ID fields into your choice of software as text since some of the IDs can otherwise be misinterpreted as long integer field types when they contain alpha characters. A null value (or blank) in the “AnalyticalResultValue” field of the text files indicates the result was less than the UCMR minimum reporting level (MRL). The “AnalyticalResultSign” field also indicates whether the analytical result is less than (<) the UCMR MRL or equal to (=) a numeric value at or above the UCMR MRL, which would be reported under “AnalyticalResultValue.” 

   Results at or above the UCMR MRL are provided in micrograms per liter (µg/L, or parts per billion). Each record represents a single analytical result measure for one contaminant in drinking water for one sampling location and sampling event from a PWS. After reporting UCMR 5 monitoring results, water providers may take action to reduce contaminant levels in finished drinking water.

   Detailed instructions for accessing results and a video demonstration of the UCMR 5 Data Finder are available on the UCMR Occurrence Data webpage. Additional data considerations and data definitions are provided in the UCMR 5 Data Summary. If you are looking for results from past UCMR monitoring (UCMR 1-4), you can find them using the UCMR Archival Data Finder.

8. How do I import the UCMR data text files into Excel? 

   Please refer to the document “Instructions for Accessing UCMR Results”. Specific UCMR analytical results can also be searched for and downloaded as an Excel file (.xlsx) using the UCMR 5 Data Finder and UCMR Archival Data Finder.

9. I don’t see UCMR 5 results for a particular PWS. Where are they? 

   If you cannot find results for a public water system (PWS):

   • The PWS may serve less than 3,300 individuals and was not selected for UCMR 5 monitoring as part of the nationally representative random sample of 800 PWSs serving that size group.
   • The PWS may be a transient non-community water system (TNCWS). UCMR 5 requirements applied to community water systems (CWSs) and non-transient non-community water systems (NTNCWSs).
   • In the UCMR 5 Data Finder, “<MRL” in the “Result” field indicates the result was less than the UCMR minimum reporting level (MRL). Only analytical results at or above the UCMR 5 MRL are reported to the EPA.
   • In the text files, a null value (or blank) in the “AnalyticalResultValue” field indicates the result was less than the UCMR MRL. The “AnalyticalResultSign” field also indicates whether the analytical result is less than (<) the UCMR MRL or equal to (=) a numeric value at or above the UCMR MRL, which would be reported under “AnalyticalResultValue.” See the UCMR 5 Data Summary for more information.

10. How does the EPA ensure that the UCMR laboratory data are accurate? 

    Only laboratories that were approved for UCMR participation through EPA’s Laboratory Approval Program, which includes laboratory Proficiency Testing, can analyze samples for the UCMR program. In addition, when a laboratory enters results into the UCMR data reporting system (SDWARS) on behalf of the PWS, they must also enter all associated method quality control (QC) data that apply to the sample results. All data fields in SDWARS have built-in QC checks to ensure all data uploaded by approved laboratories meet the analytical method and UCMR reporting guidelines.

11. What visualization tools are available to view PFAS occurrence data? 

    The publicly available PFAS Analytic Tools on EPA’s Enforcement and Compliance History Online (ECHO) webpage are integrated data visualizations that can be used to evaluate what is known about PFAS manufacture, release, and occurrence in communities. EPA’s PFAS Analytic Tools integrate data from many sources including UCMR 3 monitoring for six PFAS and UCMR 5 monitoring for 29 PFAS.

12. Where can I find more information about PFAS in drinking water? 
    • EPA PFAS Explained
      • Español: https://espanol.epa.gov/espanol/informacion-basica-sobre-pfas
    • EPA PFAS National Primary Drinking Water Regulation (NPDWR) and Supporting Materials
    • EPA PFAS NPDWR Implementation Resources

13. What are the environmental sources and uses of lithium? 

    Lithium is a naturally occurring metal in Earth’s crust. Lithium may be found at higher concentrations in certain parts of the country, particularly in groundwater sources in arid locations in the Western U.S. Lithium has numerous commercial uses including as a pharmaceutical drug, an industrial chemical catalyst, a sanitizing agent for swimming pools and hot tubs, and increasingly as a component of batteries. Lithium is likely present in a variety of foods (such as cereal grains, leafy vegetables, and root crops), but it is not clear which foods may be significant sources of dietary lithium. There is currently no U.S. recommended dietary allowance for lithium.

14. Why was lithium included in UCMR 5 and what information is available? 

    Lithium is on the EPA’s Fifth Contaminant Candidate List (CCL 5), a list of contaminants that are currently not subject to any proposed or promulgated National Primary Drinking Water Regulations (NPDWRs) but are known or anticipated to occur in public water systems (PWSs). Contaminants listed on the CCL may require future regulation under the Safe Drinking Water Act (SDWA). The EPA uses the CCL to identify priority contaminants for regulatory decision making and information collection needs. Lithium was selected for UCMR 5 through a contaminant prioritization process that considered expected or known occurrence in drinking water and the availability of health effects information. To learn more about the prioritization of lithium for UCMR 5, refer to the Information Compendium for Contaminants.

    The EPA does not have a health advisory for lithium in drinking water. However, the CCL program derived a health reference level (HRL) for screening purposes based on the EPA’s provisional peer-reviewed toxicity value (PPRTV) assessment for lithium. HRLs are not final determinations about the level of a contaminant in drinking water that is necessary to protect any particular population. The HRL for lithium is based on adverse effects observed in patients administered lithium therapeutically. Lithium has been used in pharmaceuticals for decades to treat certain medical conditions. Despite the abundance of information on patients receiving lithium at therapeutic levels, there has historically been limited information available to evaluate health risks in people at the levels associated with typical drinking water consumption. This is one of the reasons the EPA is choosing to monitor for the presence and levels of lithium in drinking water systems around the country. The science on lithium’s effects on human health, and at what levels, is still evolving.

    The EPA has developed a  Technical Fact Sheet: Lithium in Drinking Water (pdf) (270.84 KB) to help primacy agencies interpret the UCMR 5 monitoring results, understand health risks based on available information, and respond to public inquiries. For more information, please refer to the EPA’s provisional peer-reviewed toxicity value (PPRTV) assessment for lithium, the CCL 5 and Draft CCL 6 supporting materials, and the UCMR 5 Data Summary. The agency has published details regarding the removal efficiencies for various technology types via its Drinking Water Treatability Database.

15. How can lithium be removed from drinking water? 

    Lithium cannot be removed by heating, boiling, or disinfecting water. Certain drinking water treatments can reduce lithium in drinking water. Available literature, based largely on bench- and pilot-scale research, suggests that ion exchange is effective for removing lithium from drinking water. Adsorption with novel media can also be effective. The EPA has published details regarding the removal efficiencies for various technology types via its Drinking Water Treatability Database.

    The U.S. Food and Drug Administration (FDA) has not established a standard for lithium in bottled water. The FDA bottled water resources are available on the Bottled Water Everywhere: Keeping it Safe webpage.

UCMR 5 Scope, Analytical Methods, and Contaminants

Assessment Monitoring (AM)

Public water systems (PWSs) subject to UCMR 5 monitoring included:

• All community water systems (CWSs) and non-transient non-community water systems (NTNCWSs) serving more than 10,000 people
• All CWSs and NTNCWSs serving 3,300 to 10,000 people
• A representative sample of 800 CWSs or NTNCWSs serving fewer than 3,300 people
  • PWS Types

PWSs monitored for 29 per- and polyfluoroalkyl substances (PFAS) and lithium during a 12-month period from January 2023 through December 2025. See table below for the monitoring design.

Table 1. Monitoring Design

SDWA was amended by Section 7311 of the National Defense Authorization Act (NDAA) for Fiscal Year 2020. NDAA specified that the EPA shall include all PFAS in UCMR 5 for which a drinking water method had been validated, and that were not subject to a National Primary Drinking Water Regulation. In addition to lithium, UCMR 5 included all 29 PFAS that are within the scope of EPA Methods 533 and 537.1; see Table 2.

Table 2. Contaminants, Minimum Reporting Levels, Sampling Locations, and Analytical Methods

Notes

1. Chemical Abstracts Service Registry Number (CASRN)
2. The EPA-established UCMR Minimum Reporting Level (MRL) is the lowest concentration that laboratories may report to the EPA during UCMR monitoring. UCMR MRLs are determined using data from multiple laboratories that participate in the EPA’s MRL-setting studies and are not associated with contaminant health effects information. More specifically, an MRL is the quantitation limit for a contaminant that is considered achievable, with 95% confidence, by at least 75% of laboratories nationwide using a specified analytical method (recognizing that individual laboratories may be able to measure at lower levels).
3. Sample Point Location - Entry point to the distribution system (EP)
4. EPA Analytical Methods
   1. EPA Method 533
   2. EPA Method 537.1
   3. EPA Method 200.7