EPA Proposes First National Drinking Water Standard for Perchlorate: What Utilities Need to Know

The U.S. Environmental Protection Agency (EPA) has proposed a National Primary Drinking Water Regulation (NPDWR) for perchlorate, a move that could introduce new monitoring and compliance requirements for public water systems nationwide.

The proposal comes in response to a D.C. Circuit Court decision directing EPA to regulate perchlorate under the Safe Drinking Water Act. Under a consent decree, the agency must sign a final rule by May 21, 2027.

While EPA previously determined in 2020 that federal regulation of perchlorate was not warranted — citing low occurrence and high compliance costs — the court ruling requires the agency to revisit that position through formal rulemaking.

What is perchlorate and why does it matter?

Perchlorate is both a naturally occurring and manufactured chemical used in rocket fuel, fireworks, and explosives. It can interfere with iodine uptake in the thyroid, raising particular concerns for infants, pregnant women, and people with thyroid conditions.

In its proposal, EPA establishes a health-based maximum contaminant level goal (MCLG) of 0.02 mg/L (20 parts per billion, or 20,000 parts per trillion). The agency is seeking public comment on three possible enforceable MCLs:

• 0.02 mg/L (20,000 ppt)
• 0.04 mg/L (40,000 ppt)
• 0.08 mg/L (80,000 ppt)

For context, the 2024 federal PFAS MCLs range from 4 to 10 parts per trillion — orders of magnitude lower than the perchlorate levels under consideration.

EPA’s own analysis indicates perchlorate generally does not occur in most public water systems at levels posing widespread public health concern. The agency also notes that the quantified benefits of regulation may not outweigh the costs. Nevertheless, EPA is proceeding to fulfill its legal obligation and gather updated input from states, utilities, and other stakeholders.

Proposed “Binning” Approach: How Monitoring Would Work

One of the most utility-relevant elements of the proposal is a new binning system designed to reduce long-term monitoring burdens based on initial sample results.

EPA would sort systems into three bins using samples collected before the rule’s compliance date (generally three years after the final rule is issued):

Bin 1 — Lowest detections (≤ 4,000 ppt)

If all initial samples at an entry point are at or below 4,000 ppt, the system would automatically qualify for reduced monitoring of once every nine years after the compliance date.

EPA selected this threshold because it is far below even the lowest proposed MCL (20,000 ppt). However, states could still require more frequent sampling if warranted—for example, if there are known local sources of perchlorate or high variability in results.

Bin 2 — Detects above 4,000 ppt but below the MCL

Systems with any sample above 4,000 ppt but at or below the MCL would move to routine monitoring:

• Surface water systems: annual sampling
• Groundwater systems: sampling every three years

Bin 3 — Any sample above the MCL

If any sample exceeds the MCL, the system would be placed on quarterly monitoring starting at the compliance date.

How systems can move to reduced monitoring

Utilities placed in Bin 2 or 3 could eventually qualify for reduced monitoring, but only through a formal state waiver process.

At minimum, systems must first complete:

• Groundwater systems: at least two quarterly samples
• Surface water systems: at least four quarterly samples

If results show the system is “reliably and consistently” below the MCL, utilities must then complete three additional rounds of annual (surface water) or triennial (groundwater) monitoring before applying for a waiver.

Only after that sequence could a system shift to the nine-year reduced monitoring schedule.

What counts as “initial monitoring”?

A critical detail for utilities is that EPA would allow use of historical data collected after January 1, 2021, as long as samples were taken before the rule’s compliance date.

To qualify for Bin 1 from day one, systems must have already collected:

• Groundwater systems serving > 10,000 people and all surface water systems:
• Four quarterly samples at each entry point to the distribution system
• Groundwater systems serving ≤ 10,000 people:
• Two samples within a 12-month period, taken 5–7 months apart

If those records exist and meet quality requirements, systems could enter the reduced monitoring tier immediately.

EPA estimated in 2020 that perchlorate laboratory testing costs range from $55 to $175 per sample, depending on the method and laboratory used.

Rulemaking Context: The Executive Orders and Statutes Shaping EPA’s Proposal

Beyond the technical details of monitoring and compliance, EPA’s perchlorate proposal also reflects a broader regulatory landscape shaped by a series of executive orders and federal statutes spanning more than four decades — and multiple presidential administrations.

These directives do not set the perchlorate standard itself, but they frame how EPA must analyze costs, consult stakeholders, consider state authority, and weigh economic and administrative burdens while developing the rule.

Taken together, they illustrate the political and policy “zeitgeist” in which this proposal is being crafted.

A cross-administration regulatory framework

The executive orders and statutes cited in the proposal stretch from the Carter administration through President Trump’s second term, encompassing both Democratic and Republican priorities.