National Primary Drinking Water Regulations (NPDWR) – PFAS
Home / PFAS Regulations / NPDWR
Looking to navigate PFAS drinking water compliance with confidence? This page dives into the U.S. EPA’s National Primary Drinking Water Regulations (NPDWR) for PFAS. We also address several common questions about NPDWR compliance reporting and what the changes to the NPDWR proposed in 2025 may mean for drinking water systems nationwide.
WHAT ARE NPDWR?
NPDWR are legally enforceable rules intended to protect public health by limiting the levels of harmful contaminants in drinking water. NPDWR are established by the U.S. EPA under the authority of the Safe Drinking Water Act (SDWA). Limits are expressed as Maximum Contaminant Levels (MCLs) and Maximum Contaminant Level Goals (MCLGs). MCLs are the maximum permissible levels for contaminants in water. MCLGs are non-enforceable health goals set at levels at which there are no known or anticipated adverse human health effects. NPDWR also specify how often water systems need to sample and at what points in the water system.
EPA Proposes Changes to PFAS Primary Drinking Water Regulations
In May, the U.S. EPA announced plans to rescind the individual limits on HFPO-DA (GenX), PFHxS, and PFNA and the Hazard Index limit for HFPO-DA, PFHxS, PFNA, and PFBS under the NPDWR. In addition, they announced plans to extend the deadline for compliance with PFOA and PFOS Maximum Contaminant Levels (MCLs) from 2029 to 2031. The proposed rule is expected to be published in late 2025, with finalization anticipated in the spring of 2026. Until then, the current regulations and requirements reflected on this page remain in effect.
WHICH PFAS ARE COVERED BY NPDWR?
In April of 2024, the EPA established the first-ever federally enforceable standards for six PFAS in drinking water: PFOA, PFOS, PFHxS, HFPO-DA (GenX), PFNA, and PFBS. This regulation required all community water systems and non-transient, non-community water systems, regardless of the number of customers served, to monitor for six PFAS compounds. Five of these compounds have individual limits: PFOA, PFOS, PFHxS, HFPO-DA, and PFNA. Because PFAS often occur in mixtures, PFHxS, PFNA, HFPO-DA, along with PFBS are also subject to a hazard index that accounts for the presence of two or more of these compounds in a sample.
NPDWR PFAS LIMITS
| Chemical | Maximum Contaminant Level Goal (MCLG) | Maximum Contaminant Level (MCL) |
|---|---|---|
| PFOA | 0 | 4.0 ppt |
| PFOS | 0 | 4.0 ppt |
| PFNA | 10 ppt | 10 ppt |
| PFHxS | 10 ppt | 10 ppt |
| HFPO-DA (GenX chemicals) | 10 ppt | 10 ppt |
| Mixture of two or more: PFNA, PFHxS, HFPO-DA, and PFBS | Hazard Index of 1 | Hazard Index of 1 |
| Maximum Contaminant Level Goal (MCLG): The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals | ||
The Hazard Index is a tool used to evaluate potential health risks from exposure to chemical mixtures.
*ppt = Parts per trillion (also expressed as ng/L)
Source: EPA Fact Sheet, PFAS National Primary Drinking Water Regulation
HOW TO USE THE NPDWR PFAS HAZARD INDEX
In the graphic to the right, the water droplet represents the concentration of each PFAS in the sample. The denominators are called Health-Based Water Concentrations (HBWC) and represent the level at which no health effects are expected for that PFAS. If the total of all the fractions is equal to or greater than one, the water system exceeds the Hazard Index value. To be considered in violation, the running average of all samples taken in the past twelve months must also be equal to or greater than one.
NPDWR PFAS TEST METHODS
Only EPA test methods 533 and 537.1 may be used for PFAS NPDWR compliance. Many Public Water Systems (PWSs) will already be using both methods to sample drinking water as both are required to analyze for the complete set of 29 PFAS included in the Fifth Unregulated Contaminant Monitoring Rule (UCMR 5). Water systems not required to sample for UCMR 5 may choose either method for NPDWR compliance.
NPDWR PFAS MONITORING REQUIREMENTS
Initial monitoring requirements are based on the size of the water system and the source water used. Water is monitored at entry points to the distribution system, and combined water samples are not allowed. The EPA has said that data from UCMR 5 sampling may suffice for all or some of the initial monitoring requirements. Groundwater systems that serve >10,000 consumers will be required to sample for two additional quarters in addition to their UCMR 5 sampling. In addition, some states have monitoring rules that may also satisfy the requirements if the analysis was conducted using EPA Method 533 or 537.1.
Trigger Levels are used to determine if a system may reduce monitoring (triennial sampling) thereafter. The trigger levels are set at half the MCLs. If all initial sampling test results are below trigger levels, then a system may sample triennially. Otherwise, quarterly sampling is required.
NPDWR ENFORCEMENT TIMELINE
Water systems have until April 2027 to comply with the initial sample requirements
and until April 2029 to address levels of PFAS that exceed the MCLs.
STATE RULES STILL APPLY
Several states have already established enforceable drinking water limits. Any limits set by the state will remain in effect until the NPDWR PFAS limits become enforceable in 2029. For example, if a state has a drinking water limit of 10 ppt for PFOA, water systems covered under that regulation are still required to comply until April of 2029 unless the state alters or abolishes that requirement.
States will continue to be free to set their own limits, provided they are no less stringent than the federal limits. That is, a state may set a new drinking water limit that is higher than the national primary drinking water limits until April of 2029. After that, PWSs will be required to comply with the lowest limits, whether they be state or federal. States may also set limits on PFAS not covered by the NPDWR.
A LABORATORY PARTNER YOU CAN COUNT ON
With more than 40 drinking water laboratories across the country, Pace® is your go-to partner in North America for the analysis of drinking water. You can count on us to provide:
- Reliable Data. Pace® uses only EPA-approved methods 533 and 537.1 for the analysis of drinking water for NPDWR compliance. With Pace® you can count on:
- Confidential Results. We will never divulge client information to outside entities without your express permission.
- Immediate Notification. When NPDWR drinking water limits for PFAS are exceeded, we will notify you immediately.
- Self-Service Access. Our secure customer portal allows clients 24/7/365 near-real-time access to their data.
PFAS NPDWR FAQs
Q: When do drinking water systems need to start monitoring for PFAS under the NPDWR?
There is no single federal “start date” for the required Initial Monitoring under the NPDWR, but systems should begin sampling early enough to complete the required 12-month monitoring period by April 26, 2027. In practice, utilities are advised to begin Initial Monitoring by early 2026 at the latest, so there is sufficient time to collect all required samples, address any laboratory or scheduling issues, and still meet the 2027 completion deadline.
Q: What are the PFAS sampling requirements, and how will they be impacted by the proposed changes to the PFAS drinking water regulations?
PFAS sampling requirements are broken down into two phases, but requirements differ by system size:
Initial Monitoring window: All community water systems and non-transient non-community water systems must complete Initial Monitoring no later than April 26, 2027. Large systems (>10,000 consumers) and all surface-water systems regardless of size must collect four quarterly samples over a 12-month period, while smaller groundwater systems must collect two samples 5–7 months apart within a 12-month period.
Ongoing monitoring: Once Initial Monitoring is completed, systems must conduct ongoing compliance monitoring. The NPDWR calls for quarterly monitoring at first, regardless of water system size, with possible reductions in sampling frequency based on results. Primacy agencies may implement more stringent requirements.
As proposed, the changes to the PFAS NPDWR extend the deadlines for meeting MCLs, but they do not change the initial or routine monitoring windows set in the 2024 rule.
Q: Do the NPDWR requirements differ for groundwater versus surface water systems?
Yes, the PFAS NPDWR requirements differ somewhat by source water type and for consecutive systems. All community and non-transient non-community systems must complete initial PFAS monitoring at every entry point, but surface water (and GWUDI or mixed-source) systems and large groundwater systems must collect four quarterly samples in a year, while small groundwater systems (serving 10,000 or fewer people) need only two samples 5–7 months apart.
Q: Do the NPDWR requirements differ for consecutive systems that buy finished water?
Consecutive systems that only receive finished water through interconnections still must comply with the PFAS NPDWR, but their monitoring requirements are reduced because the wholesale system is responsible for sampling at the entry point to the distribution system; interconnection points themselves are not treated as entry points under the rule.
Q: When are the proposed changes to the PFAS NPDWR expected to be finalized?
EPA currently projects that the changes to the PFAS NPDWR proposed in 2025 will be finalized in the spring of 2026, with several sources citing an April 2026 target for the final rule. However, keep in mind that the proposal details and EPA schedule may change. Until then, the PFAS drinking water regulations finalized in 2024 remain in effect. It’s worth noting that EPA’s effort to rescind 4 of the MCLs is being challenged in court with some success as of Q1 2026.
Q: If the contaminants we need to report are going to change, should we still analyze for PFHxS, PFNA, GenX, and PFBS?
Yes. Systems should continue sampling and reporting for all PFAS currently required by the PFAS NPDWR until the rule is formally changed, and your primacy agency (typically your state drinking water authority) issues updated instructions. The existing regulation is still in force, so monitoring and reporting for PFHxS, PFNA, GenX, and the Hazard Index mixture remain mandatory for both initial and compliance monitoring.
It’s important to remember that EPA’s 2025 announcement about rescinding some PFAS MCLs only signifies the agency’s intent. Any actual change must go through the full notice-and-comment rulemaking process. In addition, some states are codifying the 2024 NPDWR for PFAS into state law. Until any changes are finalized and published in the Federal Record, the current NPDWR remains in force.
Q: What is a primacy agency?
A primacy agency is a government entity that has primary enforcement responsibility for public drinking water regulations under the Safe Drinking Water Act. The agency can be a state, territory, tribe, but in all cases, it must meet federal requirements as outlined in 40 CFR Part 142 and related guidance and ensure its rules are at least as stringent as EPA’s national standards.
For NPDWR compliance, all U.S. states and territories except Wyoming and the District of Columbia have been approved for primacy, meaning those two jurisdictions are directly overseen by EPA regional offices for public water system supervision. In addition, one tribe—the Navajo Nation—has primacy for public water systems on its lands, while EPA serves as the primacy agency for all other tribal lands, directly implementing and enforcing drinking water regulations there. A current list of primacy agencies under the Safe Drinking Water Act can be found on the EPA’s Annual Public Water Systems Compliance Report webpage.
Q: Can PFAS sampling frequency be reduced if results are consistently below the standards?
Under the NPDWR, sampling frequency can be reduced in two ways when PFAS results stay below “Trigger Levels”, which are set at one-half of each PFAS MCL, or when results are between Trigger Levels and MCLs in a Running Annual Average calculation:
- To move from quarterly to annual monitoring at an entry point, at least four consecutive quarterly samples are “reliably and consistently” below the PFAS MCLs.
- To move to triennial monitoring (one sample every three years), a system has two main pathways: either all Initial Monitoring results at that entry point are below the Trigger Levels, or the system is already on annual monitoring and has three consecutive annual samples below the Trigger Levels for all regulated PFAS.
Within the framework of these rule-based thresholds, the primacy agency ultimately decides whether a given entry point is eligible for annual or triennial monitoring.
Q: What are Health-Based Water Concentration values?
EPA developed Health-Based Water Concentration values to represent the concentration of a specific PFAS in drinking water below which no adverse health effects are expected. In the current PFAS NPDWR, Health-Based Water Concentrations are used as the denominators in the Hazard Index calculation for PFHxS, PFNA, HFPO-DA (GenX), and PFBS. Each measured PFAS level is expressed as a fraction of its Health-Based Water Concentration and then totaled for a Hazard Index value. When the Hazard Index value is 1 or greater, the mixture is considered to exceed the health-based standard.
The current proposal is to vacate the MCLs and Hazard Index for PFHxS, PFNA, GenX (HFPO-DA), and PFBS, while keeping only the individual MCLs for PFOA and PFOS. If these changes go into effect as proposed, the Health-Based Water Concentration values will no longer be used in the federal PFAS drinking water rule, because the Hazard Index standard that relies on them is no longer being used for PFAS.
Q: Which treatment technologies does EPA consider most effective for treating PFAS in drinking water?
EPA has identified four primary technologies as the Best Available Technologies (BATs) for treating PFAS in drinking water: granular activated carbon (GAC), anion-exchange (IX) resins, reverse osmosis (RO), and nanofiltration (NF). However, every water system is different, and water chemistry can significantly affect treatment performance and long-term operating costs.
Pace® PFAS Treatability Studies help operators compare and refine treatment options. In a treatability study, site-specific water samples are tested with different media (e.g., multiple GAC products or IX resins) and operating conditions to evaluate PFAS removal, media life, and residuals management needs. Using these performance data alongside planning-level cost estimates, utilities can compare life-cycle costs and treatment effectiveness to select a treatment approach that best fits their budget while still reliably meeting the PFAS NPDWR MCLs.
Q: Which PFAS drinking water treatment methods are most affordable for small systems with limited budget and resources?
EPA refers to their Best Available Technologies for small systems as Small System Compliance Technologies (SSCTs), with ion exchange (IX) and granular activated carbon (GAC) often providing the best balance between capital cost, operational complexity, and waste management requirements. Because water chemistry can vary significantly from one system to another, a PFAS treatability study can help ensure that limited budgets are used most effectively.
Q: Is there funding available to help with costs of monitoring and treatment?
Yes. EPA and many states have dedicated funding to help small systems and those in disadvantaged communities design and install PFAS treatment solutions. EPA’s Emerging Contaminants in Small or Disadvantaged Communities (EC-SDC) grant program provided nearly $1 billion in FY 2025 to help states and territories address PFAS and other emerging contaminants in drinking water.
In addition, the National Rural Water Association’s (NRWA) PFAS Cost Recovery Program helps eligible public water systems access settlement funds to offset PFAS-related testing, treatment, and remediation costs. There is no cost to register, and award amounts are based on PFAS levels and system flow.
Contact your primacy agency to see if there is an NPDWR-compliance assistance program for water systems in your state.
Q: Which PFAS test methods are required for NPDWR compliance?
The final PFAS NPDWR incorporates EPA 533 and 537.1 as the approved analytical methods for regulated PFAS in finished drinking water. All compliance analyses must be performed using one of these approved methods to be considered valid for NPDWR reporting purposes. Other PFAS methods, such as EPA 1633A, may be used for investigative or non-regulatory work, but the results cannot be used for NPDWR compliance reporting.
Q: Why would I use EPA 533 for NPDWR compliance versus EPA 537.1 – or vice versa?
Many public water systems use both EPA 533 and EPA 537.1 because together they cover all 29 PFAS targeted under UCMR 5. In addition, using both methods provides broader analytical coverage. EPA 533 can analyze for more short-chain and emerging PFAS. EPA 537.1 is stronger for a core group of long-chain, “legacy” PFAS and well-studied replacement PFAS, so systems often rely on it when they want continuity with past monitoring records, consistent trend analysis, and alignment with long-standing toxicological benchmarks.
| EPA 533 | EPA 537.1 | |
|---|---|---|
| Total analytes | 25 PFAS | 18 PFAS |
| PFAS common to both | 14 | 14 |
| PFAS unique to method | 11 | 4 |
| Method advantages | More short chain/emerging PFAS | More long-chain/legacy PFAS, including replacement PFAS |
Q: Can we use UCMR 5 sampling results for NPDWR compliance reporting?
EPA states that UCMR 5 results for PFAS “do not indicate compliance or noncompliance with the MCLs,” and that compliance will instead be based on running annual averages of quarterly compliance monitoring results reported to the primacy agency. However, utilities may be able to use UCMR 5 PFAS data to satisfy some or all of the NPDWR’s initial monitoring requirements, if approved by the primacy agency and the data meet conditions for rules such as timing, methods, and locations. For ongoing compliance reporting, dedicated NPDWR compliance monitoring is still required, though prior UCMR 5 results can inform monitoring frequency and planning.
Q: Do we need to use an EPA-approved lab for NPDWR compliance reporting?
Yes. For NPDWR compliance, drinking water samples used for regulatory monitoring must be analyzed by a laboratory that is certified by EPA or your state “primacy” agency, using EPA 533 or EPA 537.1 test methods. Many states will certify out-of-state laboratories, so the nearest state-certified lab may not be in your state.
Pace® maintains state certifications/accreditation in all states with a laboratory accreditation program. Contact us for a quote or to find the closest Pace® drinking water laboratory.
Q: Do the national PFAS drinking water regulations include any specific requirements for reporting results to the public?
Yes. Community water systems must include regulated PFAS monitoring results in their annual Consumer Confidence Reports starting with reports delivered after April 26, 2027, and must use required health-effects language when PFAS are detected or exceed Maximum Contaminant Levels.
In addition, systems must issue public notifications under existing Subpart Q rules whenever there are PFAS monitoring, testing-procedure, or MCL violations, using tiered timing and delivery methods designed to reach all persons served. Starting in 2029 under the current NPDWR, if PFAS levels exceed the MCLs, systems must take corrective action and promptly notify customers of the exceedance, associated health risks, and steps being taken to reduce PFAS in the water.
Q: If we use a method that analyzes for unregulated PFAS, do we need to report those results as well?
Under the PFAS NPDWR, water systems are only required to report results for the six PFAS that are regulated by the rule (PFOA, PFOS, PFHxS, PFNA, HFPO-DA/GenX, and mixtures via the Hazard Index), using the approved EPA methods and reporting formats. Results for any additional, unregulated PFAS that happen to be measured are not required to be reported for federal NPDWR compliance, although your state primacy agency may encourage or require sharing those results.
Q: Are there special sampling protocols to avoid PFAS cross-contamination that could cause false positives or inflated results?
Because PFAS are commonly found in everyday products, primacy agencies frequently recommend or require special PFAS sampling protocols to minimize cross-contamination that could lead to false positives or biased high results. Check with your primacy agency for specific sampling protocols required by your state. If you have questions, feel free to reach out to us for additional guidance.
Q: What is a Practical Quantitation Limit, and how does it apply to the NPDWR reporting?
A Practical Quantitation Limit (PQL) is the lowest concentration of a contaminant that laboratories can reliably measure with the required precision and accuracy under routine conditions using the approved methods. For PFAS NPDWR reporting, systems must submit all laboratory results (including values below the PQL) to the primacy agency, but when calculating the running annual average used to determine MCL compliance, any individual result that is less than the PQL is treated as zero in the averaging. EPA also recommends that laboratories treat results below one-third of the PQL as non-detect for reporting to systems to reduce the chance of trace background contamination artificially inflating reported concentrations.
Additional Resources for NPDWR Sampling and Reporting Compliance
- EPA Guide: Requirements and Best Practices for the Collection and Analysis of Samples for the PFAS National Primary Drinking Water Regulation
- EPA: PFAS National Primary Drinking Water Regulation FAQs for Drinking Water Primacy Agencies
- EPA Fact Sheet: Final PFAS National Primary Drinking Water Regulation: Monitoring and Reporting, April 2024
- EPA Quick Reference Guide: Initial NPDWR PFAS Monitoring
- Federal Register: PFAS National Primary Drinking Water Regulation
REASONS TO CHOOSE PACE®
EXPERIENCED
Pace® has been an industry leader in persistent organic pollutant testing for over three decades.
CERTIFIED
We’re certified/accredited by NELAC, ISO, DOD, DOE, and in every state with a PFAS lab certification program.
RELIABLE
For emergencies, our Rapid Response Team can provide defensible results in as little as 24 hours.
COMMITTED
We are committed to helping our customers advance their important work through building strong relationships, delivering upon expectations, and providing exceptional customer service.
ADVANCED
We can test for PFAS in both solid and aqueous matrices, including potable and non-potable waters, soils, and biota.
INNOVATIVE
We’re on the leading edge of science, working with EPA, DOD, ASTM, and others to develop new methods for analyzing PFAS.
