PFAS

PFAS Monitoring Requirements for Community Water Systems

A Plain-Language Summary of California General Order DW-2025-0002-DDW

Issued December 12, 2025 | California State Water Resources Control Board, Division of Drinking Water

Note: This order does not apply to Public Water Systems (PWS) which is covered under a separate General Order (2022-001-DDW)

1. What Is This Order and Who Does It Apply To?

On December 12, 2025, the California State Water Resources Control Board’s Division of Drinking Water (DDW) issued General Order DW-2025-0002-DDW. This Order requires certain public water systems across California to test their drinking water sources for per- and polyfluoroalkyl substances — commonly known as PFAS, or “forever chemicals.”

PFAS are a large family of man-made chemicals that have been used for decades in products like non-stick cookware, water-resistant clothing, food packaging, and firefighting foam. They are called “forever chemicals” because they do not break down naturally in the environment or in the human body. Exposure to PFAS in drinking water has been linked to health effects including immune system impacts, hormonal disruption, increased risk of certain cancers, and developmental effects in children.

This Order applies to two types of public water systems:

  • Community Water Systems (CWS)
    These are water systems that serve the same residential customers year-round — for example, a city or county water utility, or a homeowner association water system.
    •  
  • Nontransient Noncommunity Water Systems (NTNCWS)
    These are water systems that regularly serve at least 25 of the same non-residential people for at least six months per year — for example, schools, workplaces, hospitals, or factories that operate their own water supply.

Key Point

If your water system is a CWS or NTNCWS with active water sources, this Order applies to you. Complying with it also fulfills your obligations under the U.S. EPA’s federal PFAS National Primary Drinking Water Regulation, which was finalized on April 26, 2024.

2. What Chemicals Do You Need to Test For?

The Order requires initial monitoring of the following PFAS chains:

  • PFOA – Perfluorooctanoic acid
  • PFOS – Perfluorooctane sulfonate
  • PFHxS – Perfluorohexane sulfonic acid
  • PFHxA – Perfluorohexanoic acid

The Order requires water systems to test for PFAS using one or both of the following U.S. EPA laboratory methods:

  • EPA Method 533 — covers a broad list of PFAS compounds including short-chain PFAS.
  • EPA Method 537.1, Version 2.0 — covers a slightly different list of PFAS, including many long-chain PFAS.

All testing must be conducted by a laboratory that is accredited by California’s Environmental Laboratory Accreditation Program (ELAP). Results must be submitted electronically to the California Laboratory Intake Portal (CLIP). A key rule: laboratories must report every detection, even if the concentration is very low — they cannot substitute “zero” for a small positive reading.

The specific list of chemicals that must be reported (the “analyte list”) is set out in Exhibit B of the Order.

3. How Many Samples Do You Need to Collect, and When?

The number of samples required depends on the type of water source and the size of the population your system serves. All sampling must be completed by March 31, 2027. All results must be reported to the State by April 26, 2027.

Important notes:

  • All samples must be collected under normal operating conditions — do not sample during shutdowns, maintenance, or unusual events.
  • If your system already collected qualifying PFAS data from January 1, 2019 onward (such as samples collected for EPA’s UCMR5 unregulated contaminant monitoring program), those results may count toward your initial monitoring requirement, provided they meet the Order’s technical requirements.
  • Exhibit A of the Order lists each active source and shows whether prior data already satisfies some or all of your monitoring obligation. You are receiving this information because your facility is identified as a source that hasn’t met the monitoring requirements set forth in the Order.

Sampling Deadline

All sampling must be completed by March 31, 2027. All results and reports must be submitted to the State by April 26, 2027. These are hard deadlines — missing them constitutes a violation. That could result in the shut down of the water system.

4. Notification Levels vs. Response Levels — What's the Difference?

When PFAS is detected in drinking water, the concentration detected is compared against two types of health-based advisory thresholds: a Notification Level and a Response Level. These are not the same as Maximum Contaminant Levels (MCLs) — they are advisory levels that trigger specific actions, but they carry real regulatory weight under California Health and Safety Code Section 116378.

Notification Level (NL)

Think of this as the “early warning” threshold.

If PFAS in your drinking water is detected above the Notification Level, you must:

  • Report the detection to the DDW.
  • Include the detection in your annual Consumer Confidence Report (CCR) — the water quality report provided to customers each year.

The water does not have to be taken out of service at this level, but customers must be informed.

Response Level (RL)

Think of this as the “take action” threshold.

If PFAS is confirmed above the Response Level, the water system must do one of the following:

  • Take the source out of service immediately, OR
  • Treat or blend the water to bring PFAS levels below the Response Level, OR
  • Notify the public of the exceedance within 30 days.

Quarterly public notification is also required for as long as PFAS remains above the Response Level.

The table below shows the current Notification and Response Levels for each PFAS compound covered by the Order (updated October 29, 2025):

Units explained: ppt = parts per trillion (same as nanograms per liter, or ng/L). This is an extremely small amount — one part per trillion is equivalent to one drop of water in 20 Olympic-sized swimming pools. California and U.S. EPA now regulate some PFAS at these trace levels because of concerns about health effects even at very low concentrations.

PFBS — Note on Higher Levels

Perfluorobutane Sulfonic Acid (PFBS) has significantly higher Notification and Response Levels (500 ppt and 5,000 ppt, respectively) compared to PFOA and PFOS. This reflects current science suggesting PFBS poses a lower health risk at equivalent concentrations, though it is still a regulated PFAS and must be monitored.

5. What Do You Do If PFAS Is Detected?

Any confirmed PFAS detection — even at very low levels below the Notification Level — must be reported in your system’s annual Consumer Confidence Report. Beyond that, the required actions depend on the level detected:

If your system uses treatment to reduce PFAS (such as granular activated carbon, reverse osmosis, or blending with a clean source), you may also sample the treated or blended water to determine whether levels are below the Notification or Response Level. However, you must first contact your local DDW district office for written approval of the sampling location and setup before collecting treated-water samples.

6. What Happens If Monitoring Is Not Completed by April 26, 2027?

The April 26, 2027 reporting deadline is not optional. The Order is explicit: failure to complete the required monitoring or collect the required number of samples is a violation. The consequences are serious and can escalate.

Bottom Line on the Deadline

Missing the April 26, 2027 deadline means your water system will be in violation of both state and federal law. At a minimum, you will be required to notify your customers publicly about the monitoring failure. At worst, your system could face financial penalties, permit action, or court-ordered compliance. The State Water Board has broad enforcement authority under the California Safe Drinking Water Act and will use it.

7. What Happens After the Initial Monitoring Period?

Once the initial monitoring period closes on April 26, 2027, water systems that completed monitoring move into ongoing compliance monitoring. The frequency of future monitoring depends on what your initial results showed:

  • If all of your initial samples showed PFAS concentrations below the “trigger level” (defined as one-half of the MCL for each regulated compound), your system may qualify for reduced monitoring — testing every three years rather than every quarter.
  • If any sample exceeded the trigger level, your system will move to a more frequent compliance monitoring schedule as required under the federal regulation.


This makes completing initial monitoring on time not just a legal requirement, but a practical advantage — systems that finish and show clean results will have significantly reduced ongoing monitoring burdens.

8. Key Resources and Contact Information

Full text of General Order DW-2025-0002-DDW:
Available at: www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/pfas_ddw_general_order/

Current Notification and Response Levels:
Available at: www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/NotificationLevels.html

PFAS Monitoring FAQ (DDW):
Available at: www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/pfas_ddw_general_order/docs/pfas-monitoring-faq.pdf

Questions about your system’s monitoring status (Exhibit A):
Contact your local DDW district office. District contact information is available at: www.waterboards.ca.gov/drinking_water/programs/documents/ddwem/DDWdistrictofficesmap.pdf

This summary was prepared by Stratus Engineering Associates for informational purposes. It is intended to be a plain-language guide and does not replace the full text of General Order DW-2025-0002-DDW or applicable law. Water systems should consult directly with the DDW or qualified legal and environmental counsel for compliance guidance specific to their circumstances.

Prepared April 2026  |  Stratus Engineering Associates, LLC  |  530.676.6004  |  info@stratuseng.net