Microplastics in California Drinking Water: What the 2024 Monitoring Data Means for San Fernando Valley Homeowners

What are microplastics, and why do they appear in drinking water?

Microplastics are synthetic solid particles ranging from 1 micrometer to 5 millimeters in any dimension, the size range defined by SWRCB Resolution 2022-0015. They are not a single substance. Microplastics include fragments of polyethylene, polypropylene, and polystyrene from degraded packaging; polyester and nylon fibers shed from synthetic textiles during laundering; and tire rubber crumb from road runoff. The plastic types most commonly identified in drinking water and source water studies vary by geography, but fiber and fragment categories appear across virtually every study that has used standardized detection methods.

These particles enter source water through multiple pathways. Atmospheric deposition carries airborne microplastic fibers directly onto open reservoirs and rivers. Stormwater runoff picks up tire rubber particles, plastic packaging fragments, and synthetic turf material from streets and commercial areas. Wastewater treatment plants remove a significant fraction of microplastics through conventional treatment, but residual particles pass into receiving waterways. A peer-reviewed analysis published in Environmental Science and Technology documented microplastics in drinking water sources across multiple countries and continents (Eerkes-Medrano, Thompson, and Aldridge, 2015; doi:10.1021/acs.est.5b03746), establishing that the contaminant class is not limited to any particular source region or water type.

For San Fernando Valley homeowners, understanding microplastics in drinking water begins with the same source-water context that shapes SFV tap water quality more broadly: LADWP blends Colorado River water, State Water Project water, and local groundwater from the San Fernando Valley basin, and the blend ratio shifts seasonally. Each of those source types passes through different terrain with different plastic pollution inputs before reaching treatment.

What did California AB 1672 require for microplastics monitoring?

Assembly Bill 1672, signed by Governor Gavin Newsom in October 2021, added Health and Safety Code section 116376 to California law. The bill directed the State Water Resources Control Board to develop a standard methodology to detect and quantify microplastics in drinking water, and to require large water systems to monitor using that methodology. The full text of the bill is available at leginfo.legislature.ca.gov.

Critically, AB 1672 was a monitoring mandate, not a water quality standard. The Legislature recognized that no validated, standardized method for detecting microplastics in drinking water existed at the time of enactment. The bill funded SWRCB to develop the methodology, validate it, and build the first statewide monitoring data set. That data set is the foundation on which any future California MCL would rest. An MCL cannot be set without reliable detection data, and California's program is designed to generate that data first.

No other state had enacted equivalent mandatory monitoring legislation as of 2024, making California's program the most advanced regulatory framework for microplastics in public drinking water in the United States, according to the SWRCB's Microplastics in Drinking Water program page.

What does SWRCB Resolution 2022-0015 establish?

The State Water Resources Control Board adopted Resolution 2022-0015 in June 2022 as the regulatory action that gave AB 1672's directive operational force. The resolution does three things. First, it defines microplastics for regulatory purposes as synthetic solid particles or synthetic polymer fibers between 1 micrometer and 5 millimeters in any dimension. This definition aligns with the most commonly used scientific definition while providing the specificity needed to write enforceable requirements. Second, it establishes requirements for which water systems must monitor and what they must report. Large water systems serving 10,000 or more connections are in the first phase. Third, it sets up the public reporting structure, directing that monitoring results be posted to SWRCB's online database so that the public and researchers can access the data.

The resolution also acknowledges the methodological limitations present at the time of adoption. Standardized laboratory methods for microplastics in drinking water were still maturing in 2022. SWRCB has continued to work with laboratories to refine the analytical protocols, which is why monitoring results from 2023 and 2024 may not be directly comparable to future results if methodology refinements occur. The program was designed to be iterative, building toward a consistent, validated data set over multiple monitoring cycles. The full resolution text is available at waterboards.ca.gov.

For SFV homeowners, this regulatory background matters because it explains why there is no MCL to cite. California's program is building the science, not enforcing a limit. That is different from contaminants like PFAS, where California had an MCL before the federal April 2024 rule, or perchlorate, where a 1 ppb California MCL predates the federal standard. Microplastics are at an earlier regulatory stage, which means monitoring data are available but an enforceable limit is not.

Does LADWP water contain microplastics, and what does monitoring show?

LADWP is a large water system subject to California's mandatory microplastics monitoring requirements. Like other large California utilities, LADWP began monitoring under the SWRCB program in 2023 and 2024. Monitoring results for California utilities are reported to SWRCB and are available through the SWRCB Microplastics in Drinking Water public database. Homeowners looking for LADWP-specific figures should check that database directly, as the numbers will be updated as monitoring cycles complete.

The presence of microplastics in treated tap water from large systems, including those using conventional coagulation, flocculation, sedimentation, and filtration processes, has been documented in peer-reviewed research internationally. A study published in Environmental Research (Pivokonsky et al., 2018; doi:10.1016/j.envres.2018.08.027) found microplastics in treated drinking water at two Czech treatment plants using conventional processes. Conventional treatment removed a substantial fraction of particles but did not eliminate them entirely. That finding has been replicated across multiple subsequent studies and is consistent with the scientific consensus that conventional treatment reduces but does not fully remove microplastics.

For SFV homeowners, LADWP's source water blend adds relevant context. The Colorado River, one of LADWP's two major import sources via the Metropolitan Water District, traverses heavily developed regions including metropolitan Phoenix and Las Vegas before reaching the intake. The State Water Project draws primarily from the Sacramento-San Joaquin Delta and Sierra Nevada runoff. Both source types flow through watersheds where plastic pollution inputs have been documented. Local San Fernando Valley groundwater contributes a smaller share of the blend and is drawn from a confined aquifer, which may have a different microplastics profile from open surface water sources.

The annual LADWP Consumer Confidence Report at ladwp.com/water-quality does not currently include microplastics in its regulated contaminant table because there is no MCL to report compliance against. Microplastics monitoring results will appear in the SWRCB database rather than in the utility CCR until a regulatory limit is established.

Where do microplastics in SFV tap water come from?

Source water microplastics in the SFV system enter at multiple points before and during water treatment. Atmospheric deposition is the pathway most distinctive to Southern California: the region's Santa Ana winds and general air circulation carry synthetic fibers and plastic fragments that settle onto open reservoirs, rivers, and canals. A peer-reviewed study in Nature Geoscience (Allen et al., 2019; doi:10.1038/s41561-019-0335-5) documented microplastic atmospheric deposition in the Pyrenees at levels higher than expected for a remote location, suggesting that airborne transport of plastic particles is a significant pathway even far from urban centers.

Stormwater runoff is a second major pathway. Los Angeles has the second-largest urban stormwater system in the United States, and stormwater in the LA region carries tire rubber particles, synthetic fibers, and plastic fragments from the built environment into the Los Angeles River and other waterways that eventually reach ocean or groundwater. Research from the Southern California Coastal Water Research Project has documented microplastics in LA-area stormwater, relevant because LADWP source water quality is affected by what enters the imported water system upstream.

Synthetic textile fibers deserve specific mention because they are consistently among the most common particle types identified in drinking water microplastics studies. Home laundry machines discharge wastewater containing polyester and nylon fibers; conventional wastewater treatment removes a large fraction, but residual fibers pass into receiving waterways. A study published in Environmental Science and Technology (Browne et al., 2011; doi:10.1021/es201811s) was among the first to document synthetic fiber accumulation in marine sediments adjacent to wastewater outfalls, establishing the laundry-to-waterway pathway. That research has since been extended to drinking water source studies.

Does reverse osmosis remove microplastics from tap water?

Reverse osmosis is the treatment technology most supported by the peer-reviewed literature for microplastics reduction at the point of use. RO membranes work through physical size exclusion: water molecules and very small dissolved ions pass under pressure through a semipermeable membrane, while larger particles, including microplastics above approximately 0.001 micrometers, are rejected and flushed to drain.

The same peer-reviewed study by Pivokonsky et al. (2018) cited above noted that RO is among the most effective treatment steps for microplastics removal, consistent with the membrane's physical rejection mechanism. NSF International, through the NSF/ANSI 58 standard, certifies reverse osmosis systems for point-of-use drinking water treatment. The standard tests systems against a defined contaminant list; cyst reduction certification covers particle removal at a size range consistent with microplastics.

For SFV households considering filtration, an NSF/ANSI 58-certified RO system at the kitchen tap provides reduction for microplastics alongside other contaminants that LADWP water has documented concentrations of: total dissolved solids, nitrates, perchlorate, and certain PFAS compounds. The choice between reverse osmosis and whole-house filtration depends on which contaminants are the priority: RO addresses dissolved contaminants and particles at the kitchen tap, while whole-house carbon filtration addresses taste, odor, and chloramine residual at every fixture but does not reliably remove dissolved inorganic contaminants or microplastics.

Standard activated carbon block filters, used widely in pitcher filters, refrigerator filters, and under-sink carbon systems, do not reliably remove microplastics. Carbon filtration works through adsorption of organic compounds to the carbon surface; it does not provide the size-exclusion mechanism that rejects microplastic particles at the tap. The NSF certification categories for carbon filters (NSF/ANSI 42 for taste and odor, NSF/ANSI 53 for health effects via adsorption) do not include microplastics testing because that is not the removal mechanism for those filter types. Confirm any system's certification scope at nsf.org/certified-products.

What is EPA doing about microplastics in drinking water?

EPA has not established a Maximum Contaminant Level for microplastics under the Safe Drinking Water Act as of mid-2026. EPA's focus on emerging contaminants in recent years has centered primarily on PFAS compounds, culminating in the April 2024 final rule that set MCLs for six PFAS compounds for the first time. Microplastics were not addressed in that rulemaking.

EPA has acknowledged microplastics as a topic of ongoing scientific review. The agency's Science Advisory Board and the EPA Office of Water have published research reviews on microplastics in aquatic environments, and EPA has funded research into detection methods and health effects. However, as of the date of this article, EPA has not initiated a formal regulatory determination process for microplastics under the Safe Drinking Water Act. The agency's microplastics in drinking water resource page at epa.gov provides the current summary of EPA's scientific review and regulatory posture.

The health effects of ingested microplastics are an area of active research. The World Health Organization published a review in 2019 concluding that based on available evidence, the risk to human health from microplastics in drinking water at current levels was low, but called for further research and improved monitoring methods (WHO, 2019; who.int/publications/i/item/9789241516198). Subsequent research has continued to examine potential effects of chronic low-level exposure, and the WHO review noted that the lack of standardized detection methods was a significant limiting factor in the evidence base. California's monitoring program is directly addressing that limitation at the state level.

Should SFV homeowners take action on microplastics now?

For most San Fernando Valley households on LADWP or Las Virgenes MWD service, the practical approach is a two-step one: read the monitoring data as it becomes available, and consider an NSF/ANSI 58 RO system for drinking water if reducing microplastics alongside other contaminants is a priority.

The SWRCB's public database at waterboards.ca.gov/drinking_water/certlic/drinkingwater/microplastics.html is the place to check for LADWP and LVMWD monitoring results as they become available. The data will be reported in particles per liter, and once multiple monitoring cycles accumulate, comparisons across water systems and over time will become possible. SWRCB's public database is designed to be readable without a technical background.

Private lab testing for microplastics is available but is expensive and less standardized than testing for regulated contaminants. Unlike arsenic, nitrates, or PFAS, there is no ELAP-certified lab testing pathway with a defined protocol for microplastics in California residential drinking water as of 2026. For regulated contaminants, the California Division of Drinking Water maintains a list of ELAP-certified labs at waterboards.ca.gov/drinking_water/certlic/labs/. For microplastics specifically, the SWRCB monitoring data from your utility is likely to be more reliable and representative than a private residential test at this stage of the program's development.

A free in-home water consultation is the right starting point for SFV homeowners who want to understand the full water quality picture at their address: hardness, TDS, pH, chloramine residual, and the filtration options that match their household needs and budget. Microplastics are one part of the SFV water quality story, alongside PFAS, chloramines, and the hardness that affects appliances, fixtures, and skin. A whole-picture assessment avoids the mistake of installing a single-contaminant solution while missing a more pressing issue.

Sources used in this article: California AB 1672 (2021), leginfo.legislature.ca.gov; SWRCB Resolution 2022-0015, waterboards.ca.gov; SWRCB Microplastics in Drinking Water Program; EPA: Microplastics in Drinking Water, epa.gov; WHO: Microplastics in Drinking Water (2019); Pivokonsky et al. (2018): Occurrence of microplastics in raw and treated drinking water, Environmental Research; Eerkes-Medrano, Thompson, and Aldridge (2015), Environmental Science and Technology; Allen et al. (2019): Atmospheric transport and deposition of microplastics, Nature Geoscience; Browne et al. (2011): Accumulation of microplastic on shorelines worldwide, Environmental Science and Technology; NSF International: Certified Drinking Water Treatment Systems (NSF/ANSI 58); LADWP Consumer Confidence Report, ladwp.com; California ELAP-Certified Drinking Water Laboratories.