The PFAS National Primary Drinking Water Regulation: Questions and Answers
The EPA finalized a National Primary Drinking Water Regulation (NPDWR) for six per- and polyfluoroalkyl substances (PFAS) on April 26, 2024:
- perfluorooctanoic acid (PFOA),
- perfluorooctane sulfonic acid (PFOS),
- perfluorohexane sulfonic acid (PFHxS),
- perfluorononanoic acid (PFNA),
- hexafluoropropylene oxide dimer acid (HFPO-DA, commonly known as GenX Chemicals), and
- perfluorobutane sulfonic acid (PFBS).
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Exposure to PFAS in drinking water over a long time can cause negative health effects including thyroid disruption, certain cancers, elevated cholesterol, and immune disfunction. Sensitive subpopulations include pregnant women and developing babies. This rule will prevent thousands of deaths and reduce tens of thousands of serious PFAS-attributable illnesses.
Who is affected by this rule?
All community water systems and non-transient non-community water systems.
What are the deadlines?
The EPA will assign initial monitoring to your water system in 2026 so you can meet the April 26, 2027, deadline. Your February 2026 Monitoring and Reporting Requirements Report will communicate your monitoring schedule.
Compliance monitoring is required to begin April 26, 2027, and the monitoring frequency will depend on your initial monitoring results.
Compliance with the MCLs is due by April 26, 2029. The EPA announced in May 2025 it is looking into ways to provide more time for MCL compliance (see link to the announcement at the end of this article).
What are the MCLs?
The April 2024 rule establishes individual maximum contaminant levels (MCLs) for five chemicals, and a Hazard Index MCL for protection from mixtures for two or more of four chemicals when they occur together in drinking water (i.e. co-occur). EPA announced in May 2025 that it plans to retain the MCLs for PFOA and PFOS (see link to the announcement at the end of this article).
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Chemical
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MCL
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PFOA
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4.0 ppt
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PFOS
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4.0 ppt
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PFHxS
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10 ppt*
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PFNA
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10 ppt*
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HFPO-DA (GenX chemicals)
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10 ppt*
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Mixtures of 2 or more of PFHxS, PFNA, HFPO-DA, and PFBS
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Hazard Index of 1* (unitless)
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* EPA has announced its intent to rescind the regulations and reconsider the regulatory determinations for PFHxS, PFNA, HFPO-DA (commonly known as GenX Chemicals), and the Hazard Index mixture of these three plus PFBS to ensure that the determinations and any resulting drinking water regulation follow the legal process laid out in the Safe Drinking Water Act. For more details, see the link to the announcement from May 2025 at the end of this article.
Where do I sample?
Sampling is required at all entry points to the distribution system (finished water). Each entry point may have a different monitoring schedule based on the source water type. System interconnections between a seller and purchaser are not required to be sampled.
What are the initial monitoring requirements?
Semiannual sampling is required by groundwater systems serving 10,000 or fewer persons. The two samples will be required five to seven months apart.
Quarterly samples collected two to four months apart are required for surface water systems, groundwater under the direct influence of surface water systems, groundwater systems serving more than 10,000 persons, and any entry point that blends surface water and groundwater.
What EPA analytical methods and laboratories are required?
For initial monitoring, the EPA has determined the following labs can be used. These labs must use EPA method 533, EPA method 537.1 version 1, or EPA method 537.1 version 2.
- Laboratories EPA approved for the Fifth Unregulated Contaminant Monitoring Rule (UCMR5)
- Laboratories certified by a state laboratory certification program
- National Environmental Laboratory Accreditation Program (NELAP) state accreditation programs that use the TNI standard – search for NELAP/TNI labs by method (533 or 537.1)
For compliance monitoring, laboratories must be certified by the EPA or the state and use EPA method 533 or EPA method 537.1 version 2.
Can previously acquired PFAS samples count towards the initial monitoring requirements?
Yes! Previously acquired PFAS sample results can partially or completely satisfy your initial monitoring requirements if certain conditions are met:
* A PQL is the lowest level at which a contaminant can be reliably quantified within specific limits of precision and accuracy during routine laboratory operating conditions using the approved methods. Note that samples collected prior to June 25, 2024, that were only analyzed down to the level of the MCLs are acceptable but would not qualify a system for reduced monitoring. To potentially qualify for reduced monitoring, samples must be analyzed down to half the MCLs or lower.
What are the best available technologies for treatment?
EPA does not specify or require how water systems must comply with the regulation, but the following technologies were identified as those that are capable of meeting the MCLs: granular activated carbon, anion exchange, and reverse osmosis/nanofiltration.
The EPA identifies feasible best available technologies based on factors such as high removal efficiency, reasonable cost, service life, and ability to achieve compliance.
How can I prepare for this rule?
Become familiar with the rule by reviewing available fact sheets on the regulation website and quick reference guides on the implementation website.
Prepare for logistics and establish a budget. Each sample set is approximately $309.
Sign-up to participate in WDEQ’s PFAS in Drinking Water Monitoring Assistance Program or the EPA Region 8’s Tribal Emerging Contaminants Sampling Project.
- WDEQ’s program will collect and analyze all the samples water systems will need to meet the initial monitoring requirements and provide PFAS sample collection training to operators, including on-site training, all at no cost to the water system.
- The Tribal Emerging Contaminants Sampling Project is also cost free and will collect and analyze a portion of the samples, as well as provide on-site sample collection training and webinar trainings.
What is the PFAS OUT initiative?
In May 2025, EPA announced planning for the new PFAS OUTreach initiative (PFAS OUT). Through PFAS OUT, the agency will initiate enhanced outreach to water systems known to need capital improvements to address PFAS, including those EPA has identified as having PFOA and PFOS levels above EPA’s MCL. EPA will share resources, tools, funding, and technical assistance opportunities to help utilities address PFAS. PFAS OUT will ensure that no community is left behind as we work to protect public health and bring utilities into compliance with federal drinking water standards.
What technical and financial assistance resources are available?
WaterTA supports communities to identify water challenges, develop plans, build capacity (technical, managerial, and financial), and develop application materials to access water infrastructure funding. Complete the form to request technical assistance.
Wyoming Department of Environmental Quality's (WDEQ) Emerging Contaminants in Drinking Water Grant can assist public water systems and private well owners address PFAS and other emerging contaminant-related issues in drinking water or source water. Eligible projects include monitoring, public outreach and education, source water planning, source water protection activities, planning and design, treatment, and others. Eligible entities can apply for subawards or WDEQ can conduct projects on behalf of eligible entities.
The Wyoming State Revolving Funds Program (SRF) provides funds to assist public entities with water infrastructure improvement projects. The Wyoming DEQ assists public water systems with the loan application process.
Additional programs and resources are available to local municipalities, Tribes, and communities, and additional financial resources are available. Please contact Karen Ward at ward.karen@epa.gov if you have questions about these assistance resources.
What if I have questions about the regulatory requirements or PFAS sample results I have already taken?
Contact Kendra Morrison at morrison.kendra@epa.gov or (303) 312-6145.
What is the link to EPA’s May 2025 announcement about changes the agency intends to make to the PFAS NPDWR?
See “EPA Announces It Will Keep Maximum Contaminant Levels for PFOA, PFOS”
Please note that the information provided in this article is for technical assistance only and does not supersede the rule requirements in 40 CFR 141 Subpart Z.
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