Home Water Testing: City, Well Water & Microplastics
Learn how to test city or well water, read results, and spot microplastics. The Wellness Quality Institute helps brands verify plastic-related claims.
Read articleCalifornia Microplastics Water Rules: MCLs & Basin Plans
The Wellness Quality Institute explains California's microplastics rules—MCLs, notification levels & basin plans—to keep your claims defensible.
Written by: Scott Steveson, Specialist, Wellness Quality Institute
Key Takeaways
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California’s Porter-Cologne Act and regional basin plans create the legal structure for microplastics monitoring in drinking water, including triennial reviews and waste-discharge permits.
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State maximum contaminant levels (MCLs) are enforceable limits, while notification levels are advisory triggers; results below a notification level still do not prove that a contaminant is absent.
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Two validated methods (SWB-MP1-rev1 infrared and SWB-MP2-rev1 Raman) detect particles only above 20–50 µm, so the 1–20 µm and nanoplastic ranges remain unmeasured.
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A laboratory “none detected” result is limited by the method’s detection floor and the list of polymers tested; it does not confirm that plastic is completely absent.
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Companies that want defensible claims can use their existing lab data within The Wellness Quality Institute’s Plastic-Free Pathway Verification to show verified progress.
How Porter-Cologne and Basin Plans Shape Microplastics Oversight
The Porter-Cologne Water Quality Control Act, passed by the California Legislature in 1969, significantly expanded the power and enforcement authority of the State Water Resources Control Board and nine Regional Water Quality Control Boards. It became one of the nation’s strongest anti-pollution laws and influenced parts of the 1972 federal Clean Water Act.
The Act authorizes a statewide and regional system for water-quality control, including water-quality control plans, commonly called basin plans, and a permit-based system for discharges. The focus is on preventing pollution damage rather than reacting after harm occurs.
Within this framework, the water boards issue Waste Discharge Requirements (WDRs) as state-only permits for discharges into waters of the state, which has a broader legal meaning than the federal term “Waters of the United States.” Regional boards also issue cleanup and abatement orders, cease and desist orders, and National Pollutant Discharge Elimination System (NPDES) permits.
Basin plans, which function as regional water-quality blueprints, must include three core elements. They identify beneficial uses such as municipal water supply, fish and wildlife protection, or recreational contact. They set numeric or narrative water quality objectives to protect those uses. They also include a program of implementation that outlines actions, timelines, and monitoring. Federal law requires states to review water quality standards at least once every three years, with basin plans incorporated as one element of those standards, so agencies can update them as regional conditions and policy needs change.
The table below shows how these regulatory tools connect to microplastics monitoring, from the Porter-Cologne Act through the two validated analytical methods that define what laboratories can currently measure.
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Instrument |
Governing Authority |
Primary Function |
Microplastics Relevance |
|---|---|---|---|
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Porter-Cologne Act (1969) |
Statewide and regional water-quality control, basin plans, WDRs, NPDES permits |
Provides the statutory authority under which microplastics monitoring requirements are issued |
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Basin Plans (triennial review) |
Designate beneficial uses, set water quality objectives, outline implementation programs |
May incorporate microplastics objectives as monitoring data matures |
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|
SWB-MP1-rev1 (infrared spectroscopy) |
Standard operating procedure for microplastics extraction and measurement in drinking water |
Validated detection range: >50 µm through 5,000 µm |
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|
SWB-MP2-rev1 (Raman spectroscopy) |
Standard operating procedure for microplastics measurement by Raman spectroscopy |
Validated detection range: >20 µm through 5,000 µm |
How California Uses MCLs and Notification Levels
California often sets stricter drinking-water limits than federal requirements. Chromium provides a clear example. California maintains a total chromium MCL of 50 parts per billion (ppb), while the federal total chromium standard is 100 ppb. In June 2023, the State Water Resources Control Board formally proposed a separate MCL of 10 ppb for hexavalent chromium, a more toxic form, showing how the state separates contaminants when science supports that step.
Beyond enforceable MCLs, California runs a parallel advisory system. Notification levels are health-based advisory concentrations for contaminants that lack established MCLs. They trigger public notification when exceeded but are not enforceable standards. Of 97 chemicals with notification levels, 40 now have MCLs through the formal rulemaking process, which shows how advisory levels often come before binding rules.
This two-tier structure, advisory triggers alongside enforceable limits, shapes how laboratory data should be read. A result below a notification level is not the same as a result below an MCL, and neither equals an absence of the contaminant. That careful interpretation of what a result proves is exactly what separates a defensible claim from an indefensible one.
Microplastics Definition and Method Limits
California’s formal definition of microplastics in drinking water is broad on purpose. It covers solid polymeric material with particles that have at least three dimensions greater than 1 nanometer and less than 5,000 micrometers. The State Water Resources Control Board adopted this definition in June 2020, becoming the first regulatory agency worldwide to define microplastics in drinking water. The board released standardized measurement methods in September 2021 and adopted a policy handbook in September 2022.
Two published analytical methods define what laboratories can currently measure in practice:
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SWB-MP1-rev1, which uses infrared spectroscopy and has a validated detection range of particles greater than 50 µm through 5,000 µm
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SWB-MP2-rev1, which uses Raman spectroscopy and has a validated detection range of particles greater than 20 µm through 5,000 µm
The gap between the definition and the methods is the most important technical fact in this field. The regulation covers particles down to 1 nanometer, but the best validated methods begin at 20 or 50 micrometers, which are thousands of times larger. That gap leaves the 1–20 µm fraction unvalidated under either method, and everything below 1 µm, the nanoplastic range, beyond reliable commercial measurement.
A laboratory result of “none detected” therefore means none found above the instrument’s detection floor, for the polymer types it screened, in the production lot it tested. It does not mean none present. That distinction marks the line between a defensible claim and an indefensible one.
Why Regional Water Boards Matter for Microplastics
California’s nine Regional Water Quality Control Boards exist because the state’s diversity in precipitation, topography, population, and municipal, agricultural, industrial, and recreational water demands makes uniform statewide standards impractical. Each regional board is organized around one of the state’s nine major watersheds.
Regional boards prepare basin plans tailored to local conditions and hold authority to set and enforce water quality standards, issue waste discharge permits, monitor quality, and pursue enforcement actions. Each regional board must set water quality objectives that reasonably protect beneficial uses and prevent nuisance, while considering local factors. These factors include past, present, and likely future beneficial uses of water, environmental characteristics of the hydrographic unit, water quality that is reasonably achievable, and economic considerations.
Regional variation appears in several ways. The Santa Ana Region’s tailored salt and nutrient management plan updates total dissolved solids and nitrogen objectives and waste load allocations specific to the upper and lower Santa Ana River watersheds. The Central Coast Water Board’s Basin Plan designates beneficial uses and water quality objectives for surface waters and groundwater across that distinct hydrologic region. The Bay-Delta Plan is managed directly by the State Water Resources Control Board rather than a regional board because its watershed spans multiple regions. This regional structure shapes regulatory obligations, but it does not change the technical reality companies face when they want to make a market claim: a laboratory report is not the same thing as a defensible claim.
What Laboratory Reports Actually Prove for Claims
A laboratory report and a defensible market claim are not the same thing. A reviewed dataset supports only the tested particle-size range, the polymer panel screened, which is the specific list of plastic types the instrument looked for, and the production period sampled. As established earlier, a dataset does not prove the absence of plastic below the method floor, outside the tested polymer types, or in lots that were not sampled.
This gap between having data and making a claim is the practical problem companies face. A business may hold a clean lab report, but that report alone does not authorize a market claim. It only documents what was tested, how it was tested, and what was found within those limits. Bridging that gap requires an independent review that checks data quality, methodology, and scope, then translates the technical findings into claim language that stays within what the evidence supports. The Wellness Quality Institute (WQI) was created to provide that bridge.
The Wellness Quality Institute is an independent verification body that reviews companies’ existing third-party laboratory data on plastic and microplastic content against a defined standard, so brands can substantiate real progress toward plastic-free standards instead of claiming impossible zero-plastic outcomes. WQI’s core program, Plastic-Free Pathway Verification (PFPV), governed by the standard WQI-CS-01, reviews a company’s independent laboratory dataset, testing methodology, product scope, and supporting controls against criteria focused on particle size and polymer type. These criteria align with a state water board’s drinking-water microplastics reference framework. That state framework serves as a technical reference point, not a geographic boundary, and verification is available to U.S. companies nationally. The state did not create, approve, authorize, or endorse WQI or its standard.
The review examines laboratory qualification, analytical method, product matrix, sampling approach, tested particle-size range, target polymer panel, reporting limits, blank results, spike recoveries, replicates, chain of custody, data recency, and product scope. This line-by-line examination often reveals gaps that companies did not know existed. Many discover for the first time what their existing data does and does not prove, including where a “none detected” result is limited by the method’s detection floor rather than by the product itself.
Every review produces one of two outcomes. Standard Met means the dataset satisfies all applicable technical and data-quality requirements and that no reportable target polymer particles are detected within the tested particle-size range and approved reporting limits. A non-detect result alone is not enough, because the reporting limits themselves must meet WQI requirements. If those conditions are not satisfied, the outcome is Standard Not Met. This is a private determination, never described as a failed product, and it may reflect insufficient data or an unsupported method rather than anything about the product itself. Companies can resubmit with updated information.
Products that meet the standard receive a scope-locked license to use the mark “WQI Plastic-Free Pathway Verified,” a public registry listing, and approved claim language. Verification is locked to the reviewed product, dataset, tested particle-size range, polymer panel, and production period. Companies cannot extend a single dataset to a company-wide or product-line claim. A single assessment fee covers review, verification decision, and registry listing. Independent laboratory testing is arranged and billed separately by a qualified independent laboratory.
Frequently Asked Questions
How do California notification levels differ from enforceable MCLs?
As explained earlier, a maximum contaminant level (MCL) is a legally enforceable standard, while a notification level is a health-based advisory that triggers public notification but not a regulatory violation. California also uses response levels, typically set at ten times the notification level for non-cancer endpoints, at which the Division of Drinking Water recommends removing a drinking-water source from service. The distinction matters for claim substantiation. A product result below a notification level is not the same as one below an enforceable MCL, and neither equals an absence of the contaminant.
What do California’s two validated microplastics methods measure, and what do they miss?
California’s two published standard operating procedures use different spectroscopy techniques, infrared for SWB-MP1-rev1 and Raman for SWB-MP2-rev1, to identify plastic particles by their chemical signature. As noted earlier, infrared is validated down to 50 µm and Raman to 20 µm, but neither reaches the 1–20 µm fraction or the nanoplastic range below 1 µm. California’s regulatory definition extends down to 1 nanometer, which is thousands of times smaller than either method’s lower limit. The practical result is that any “none detected” result under these methods is bounded by the instrument’s detection floor. Particles smaller than the method’s starting point are invisible to it, not confirmed absent.
Why do regional basin plans differ, and why does that matter for claims?
Each of California’s nine Regional Water Quality Control Boards prepares a basin plan tailored to the hydrology, land use, and beneficial uses of its watershed. Beneficial uses are the purposes a water body is meant to serve, such as municipal and domestic supply, agricultural irrigation, recreational contact, or fish and wildlife habitat. Water quality objectives are set to protect those uses, so they vary by region. The Santa Ana Region has a tailored salt and nutrient management plan for total dissolved solids and nitrogen in its watersheds, while the Central Coast plan addresses different surface-water and groundwater conditions. This regional variation means a water quality objective in one basin may not apply in another. For companies, it underscores that regulatory context can shift by region, while the technical limits of measurement and claim substantiation remain constant.
What does WQI Plastic-Free Pathway Verification confirm, and what does it not confirm?
WQI Plastic-Free Pathway Verification confirms that a company’s independent laboratory dataset was reviewed against WQI’s defined standard, WQI-CS-01, and that the methodology, controls, and data quality met the review criteria. It also confirms that no reportable target polymer particles were detected within the tested particle-size range and approved reporting limits for the specific product, production period, and polymer panel reviewed. As noted earlier, that scope is bounded by the method’s detection floor, the polymer panel, and the production period sampled. The mark “WQI Plastic-Free Pathway Verified” describes a verified pathway toward plastic-free standards, not a state of being plastic-free. No laboratory today can confirm the complete absence of plastic across every particle size, polymer type, and production lot, and WQI does not claim otherwise. WQI verification is not a state approval, a government certification, or a health or safety certification.
Conclusion: Turning Real Data into Defensible Progress
A state’s water-quality regulatory framework, anchored in a water quality control act, implemented through regional basin plans, and extended to microplastics through legislation, provides a stringent and method-based public reference for evaluating plastic content in water and liquid products. Its value for U.S. companies lies in technical credibility rather than geographic obligation. It offers a published definition, two validated analytical methods, and a monitoring program that makes the framework’s standards checkable instead of merely asserted.
The framework also makes the measurement gap clear. The definition reaches to 1 nanometer, while the validated methods begin at 20 or 50 micrometers. That gap is an honest statement of where the science stands today, not a failure of the framework. Any claim that ignores that gap asks the evidence to carry more than it can support.
Companies that hold genuine laboratory data and want to convert it into a defensible, scope-locked public claim have a clear path forward. The Wellness Quality Institute reviews existing datasets against WQI-CS-01, a standard aligned with a state water board’s drinking-water microplastics reference framework, and issues registry-backed verification decisions with approved claim language that stays within what the evidence supports.
WQI Plastic-Free Pathway Verification does not certify that a product contains zero plastic, microplastics, or nanoplastics. It shows that the company is on a verified pathway toward plastic-free standards. Verification applies only to the reviewed products, submitted datasets, tested ranges, polymer panels, production or sampling periods, and supporting controls. WQI verification is not a state approval, government certification, or health or safety certification.
