What the EPA actually set in April 2024

On April 10, 2024, the Environmental Protection Agency finalized the first enforceable federal drinking water standards for PFAS. The rule applies to all public water systems serving more than 25 people, about 66,000 systems nationwide.

The standards are part of the Safe Drinking Water Act. The EPA developed them under the Biden administration's PFAS Strategic Roadmap, after years of advocacy, scientific review, and public comment. The rule builds on growing evidence about PFAS health effects, including links to cancer, liver damage, immune system problems, and developmental harm in children.

The EPA set limits for six PFAS compounds. For two of them, PFOA and PFOS, the agency set the Maximum Contaminant Level Goal at zero. The MCLG is the non-enforceable health target, the level at which no adverse health effects are expected. Zero means the EPA has determined there is no level of exposure considered safe.

The enforceable limits, called Maximum Contaminant Levels, are set slightly higher because they account for what treatment technology can realistically achieve. But the zero MCLG sends a clear signal about the science.

The six regulated compounds and their limits

The EPA set Maximum Contaminant Levels for five individual PFAS compounds and one mixture standard called the Hazard Index. Here are the five individual limits:

  • PFOA (perfluorooctanoic acid): 4 parts per trillion. MCLG is zero.
  • PFOS (perfluorooctanesulfonic acid): 4 ppt. MCLG is zero.
  • PFHxS (perfluorohexanesulfonic acid): 10 ppt. MCLG is 10 ppt.
  • PFNA (perfluorononanoic acid): 10 ppt. MCLG is 10 ppt.
  • HFPO-DA (also called GenX, made by Chemours): 10 ppt. MCLG is 10 ppt.

Parts per trillion is an extremely small unit. One part per trillion is roughly one drop of water in 20 Olympic-sized swimming pools. The EPA set these limits low because PFAS are persistent in the environment and in the human body, and because exposure adds up over time.

PFOA and PFOS are the most studied PFAS. They were used for decades in firefighting foam, nonstick cookware, and stain-resistant fabrics. Both have been phased out of production in the United States, but they remain in groundwater and drinking water sources near military bases, airports, industrial sites, and landfills.

PFHxS, PFNA, and HFPO-DA are replacement chemicals. Industries introduced them as PFOA and PFOS were phased out. Research suggests they carry similar health risks.

How the Hazard Index works for mixtures

PFAS rarely show up alone. Most contaminated water contains a mix of compounds. The Hazard Index is a way to regulate that mixture. It accounts for the fact that PFAS compounds can have additive health effects.

The Hazard Index applies to four compounds: PFHxS, PFNA, HFPO-DA, and PFBS. PFBS does not have its own MCL, but it is part of the mixture calculation.

Here's how the calculation works. For each compound, you divide its measured level by its Health-Based Water Concentration. Then you add the four ratios together. If the sum is greater than 1.0, the system has exceeded the Hazard Index limit.

The Health-Based Water Concentrations are:

  • PFHxS: 10 ppt
  • PFNA: 10 ppt
  • HFPO-DA: 10 ppt
  • PFBS: 2,000 ppt

A simple example helps. Say a water system has 5 ppt of PFHxS and 5 ppt of HFPO-DA. The calculation is (5 divided by 10) plus (5 divided by 10), which equals 0.5 plus 0.5, which equals 1.0. That's exactly at the limit.

If the same system had 6 ppt of PFHxS and 6 ppt of HFPO-DA, the sum would be 1.2, which exceeds the limit. The system would be required to treat the water.

The Hazard Index matters because many contaminated systems have low levels of several PFAS compounds. Each individual compound might be below its own MCL, but together they can still pose a health risk.

When water systems have to comply

The EPA built a multi-year timeline into the rule. Water systems have time to plan, fund, and install treatment.

In 2027, water systems must complete initial monitoring for the six regulated PFAS compounds. Systems will test their sources and report results to state regulators and the EPA.

In 2029, systems that exceed any of the limits must have treatment in place to bring levels below the MCLs. They must also notify the public.

The rule also mandates ongoing public reporting. Once compliance starts, PFAS levels will appear in annual Consumer Confidence Reports. These reports are mailed or posted online every year and show what contaminants were detected in the water.

The EPA designed the timeline to give utilities time to secure funding and build infrastructure. Treatment systems for PFAS are expensive. Common methods include granular activated carbon, reverse osmosis, and ion exchange. Small and rural systems face the biggest challenges because they have fewer customers to spread costs across.

What happens if a system exceeds the limits

If a water system exceeds any of the MCLs during compliance monitoring, it must issue a public notice within 30 days. The notice must describe the violation and the steps being taken to fix it.

The utility must take action. Options include installing treatment, switching to a cleaner source, or blending contaminated water with cleaner water to dilute the levels below the MCLs.

States with their own drinking water regulators handle enforcement in most cases. The EPA can step in if a state fails to act.

Failure to comply can result in federal enforcement action and fines. But the more common outcome is a consent order that requires the utility to submit a treatment plan on a specific timeline. State and federal regulators typically work with utilities to bring them into compliance rather than immediately imposing penalties.

Utilities can apply for federal and state grants to help pay for treatment. The Bipartisan Infrastructure Law included $9 billion for PFAS cleanup and other drinking water improvements. However, funding has become uncertain.

Where the rule stands now

The April 2024 rule remains in effect, but it faces legal and political challenges.

In 2025, several industry groups, including the American Water Works Association, sued the EPA seeking to overturn or modify parts of the rule. The lawsuits argue that the cost-benefit analysis was flawed and the limits were too aggressive given current treatment technology. Litigation is ongoing in the U.S. Court of Appeals for the D.C. Circuit.

The rule remains in effect during litigation. The 2027 monitoring deadline still applies unless a court orders otherwise.

In 2025, the Trump administration's EPA cancelled hundreds of millions of dollars in grants that would have helped state and local water systems fund PFAS cleanup. Some of those cancellations are also being challenged in court. The funding cuts have left many small utilities uncertain about how they will pay for treatment if their water exceeds the limits.

Despite the uncertainty, many states are moving forward. Some states, including Michigan, New Jersey, and Vermont, have set their own PFAS limits that are stricter than the federal rule. Utilities in those states are already working on compliance.

How CheckYourWater fits in

CheckYourWater shows EPA UCMR 5 results for every public water system that has been tested. UCMR stands for Unregulated Contaminant Monitoring Rule. UCMR 5 sampling ran from 2023 to 2026 and included 29 PFAS compounds.

We grade each system A through F based on how its results compare to the April 2024 MCLs. A system that exceeds the MCLs in UCMR 5 is not yet in legal violation, because the compliance deadline is 2029. But the data is a strong indicator of what the system's Consumer Confidence Report will look like once compliance reporting begins.

The UCMR 5 data is the most full snapshot of PFAS in U.S. drinking water that exists. It covers large and small systems across all 50 states. CheckYourWater turns that data into plain-language reporting so you can see what's in the water serving you.

Enter your zip code at checkyourwater.org to see your local results.