The regulation of PFAS in California, as exemplified by policies such as SB-46, SB-1371, SB-530, SB-756, SB-170, SB-154, AB-180, and AB-178 (see Table 1 for descriptions and date of adoption), has been instrumental in addressing the issue of PFAS contamination in drinking water. Primarily, SB-756 set Maximum Contaminant Levels (MCLs) for certain PFAS in drinking water and mandated that water utilities must monitor and take action to reduce PFAS levels in their water sources if they exceed the specified MCLs. This proactive monitoring and remediation can lead to a reduction in PFAS contamination in drinking water. Furthermore, SB-46 aimed to regulate the use of PFAS in consumer products, including food packaging and carpet cleaners. By restricting the use of PFAS in these products and requiring companies to disclose their presence, the potential for PFAS to migrate into the environment and contaminate water sources when these products are disposed of is reduced. Additionally, SB-530, SB-170, SB-154, AB-180, and AB-178 provided financial support to water utilities to expedite the remediation of drinking water sources contaminated with PFAS. Faster remediation means that contaminated sources are taken out of service more quickly and fixed, ultimately reducing water contamination.

Our analysis of the water contamination data obtained from the California State Water Resources Control Board indicates a significant decline in PFAS concentrations between the pre-legislation (2017) and post-legislation (2023) periods—a trend that coincides with the implementation of policies such as SB-756, SB-46, AB-756, and SB-530. However, because our study relies on a comparison of means using unpaired and Welch’s t-tests, we cannot conclusively attribute the observed decline solely to these legislative measures. Other factors—including changes in industrial practices, advancements in water treatment technologies, or natural variations in PFAS levels in water sources—may also have played a role. Although our findings suggest that these policies may have contributed to the observed decline in PFOA and PFOS levels, the lack of PFOA and PFOS contamination data in UCMR 4 [14] (recorded in the years between 2017 and 2023) and compliance data from specific sites research hinders our ability to conduct more rigorous causal inference methods such as interrupted time series, difference-in-differences, and panel data regression analysis. Conducting these analyses could strengthen the relationship between legislative action and water quality improvements.

After evaluating the impact of legislation passed in California from 2018 to 2023 on PFAS water contamination levels, we can see that some progress has been made in addressing this pressing issue. However, there remains room for improvement and the implementation of further measures to ensure continued reduction in PFAS contamination. One promising avenue for future legislation is the establishment of stricter industrial controls for waste streams. Industries that use or produce PFAS-related substances must be held accountable for managing their waste and emissions more responsibly [15]. These controls could include mandatory treatment of industrial wastewater to remove PFAS before discharge and incentives for adopting safer alternatives to PFAS in products. Ultimately, there is a need for a zero-waste hierarchy and a need to push industry toward adopting a circularity model as a path to reducing environmental health harms from PFAS.

Moreover, we recommend that the California state government collaborates with advocacy groups like the Environmental Working Group (EWG) and the Center for Environmental Health (CEH) to strengthen advocacy efforts and ensure that the concerns of residents are heard while passing legislation. In California, EWG has been instrumental in pushing for state-level legislation for greater transparency and stricter standards regarding the presence of harmful chemicals in consumer products, water, and food. They have conducted several studies highlighting issues specific to California. CEH is headquartered in California. Their work in the state involves safeguarding residents from toxic chemicals in various areas, including consumer products and drinking water. Their focus areas include climate and energy, water, urban land use, and conservation of lands and wildlife in the San Francisco Bay Area. By collaborating with these advocacy groups, California can gain a better understanding of the status quo and what its residents truly want, hence improving the quality of the legislation passed.

States like California, with demonstrated commitment to PFAS regulation, can serve as models for other states and the federal government. Under the Safe Drinking Water Act, the EPA has the authority to set enforceable National Primary Drinking Water Regulations (NPDWRs) for drinking water contaminants and require monitoring of public water systems [16]. With this authority, on 10 April 2024, the EPA announced the final NPDWR for six PFAS chemicals: PFOA, PFOS, PFHxS, PFNA, HFPO-DA (commonly known as GenX Chemicals), and mixtures containing two or more of PFHxS, PFNA, HFPO-DA, and PFBS [17]. In our view, the EPA’s regulatory efforts could be further strengthened by adopting some of the more rigorous standards pioneered by California. For example, SB-46 regulated the use of PFAS in consumer products and wastewater discharges. The bill required companies to disclose the presence of PFAS in their products and restrict the use of certain PFAS chemicals in food packaging, carpet cleaners, and other products. By mandating product-level disclosure and imposing targeted restrictions, SB-46 directly curtails the primary pathways through which PFAS enter the environment and reduces consumer exposure to these chemicals. Moreover, if the EPA were to adopt similar measures nationally, it would enable the systematic reduction of PFAS emissions from both industrial and consumer sources, thereby decreasing the overall environmental burden of PFAS and substantially mitigating the associated health risks. In addition to the enforceable standards set under the Safe Drinking Water Act, the Toxic Substances Control Act (TSCA) provides the EPA with critical authority to gather comprehensive data on the manufacture, import, and use of PFAS. Recent TSCA mandates that any entity that has manufactured PFAS in any year since 2011 will need to report their data to EPA through Central Data Exchange (CDX) [18]. This enables the EPA to map out novel and crucial pathways through which these chemicals enter the environment—especially into drinking water systems. With this dataset in hand, the EPA could take further action, similar to its restrictions on polychlorinated biphenyls (PCBs) in 1979 [19], which are also endocrine-disrupting chemicals that can interrupt hormone delivery and circadian rhythm [20, 21], to impose targeted bans or limitations on PFAS uses that are found to contribute significantly to environmental contamination and public health risks.

Building on these state-level successes, cooperation among states and collaboration with the federal government—particularly in Congress and the EPA—can facilitate the development of a comprehensive national framework. As demonstrated by California’s rigorous PFAS regulatory measures, which our analysis shows may have led to significant reductions in PFAS contamination in drinking water, the federal government can adopt similar standards to benefit the nation. National policies modeled on California’s example would provide critical guidance and support to states that have enacted less stringent PFAS legislation. By implementing policies similar to California’s, Congress and the EPA could streamline compliance for industries and utilities, reduce environmental disparities among states, and substantially mitigate the public health risks associated with PFAS exposure throughout the country.

Our study spans a period of several years, allowing for a robust comparison between pre-legislation and post-legislation periods, offering valuable insights into the impact of legislative changes. The study relies on official data collected by the California State Water Resources Control Board, enhancing the reliability and credibility of the findings. The research methodology is transparent and replicable by focusing on specific PFAS chemicals and using established cutoff points for contamination levels. The study’s comparative analysis approach is also a strength. By comparing PFAS contamination levels before and after the introduction of legislation, the study offers a clear indication of the potential impact of regulatory measures on water quality. We had a robust review and policy analysis of relevant legislation. The study goes beyond data analysis to provide valuable policy recommendations for addressing PFAS contamination. It offers a forward-looking perspective on potential avenues for future legislation, which can guide policymakers and stakeholders in addressing this complex issue.

It is essential to acknowledge the potential limitations of the study, including the fact that while testing has covered half of the population in California, as of 2023 it only represents 3% of public water systems in the state [2]. Many small public water systems and private wells are not included in the monitoring program, leaving over 19 million Californians’ water untested for PFAS [2]. This lack of testing means that the actual extent of PFAS pollution in the state is likely far more significant than current data suggests, especially in rural and disadvantaged communities that rely on small water systems or private wells. Moreover, California’s current testing only includes 18 PFAS chemicals, with health advisories established for only three of them. This leaves unknown data for many PFAS chemicals, making it difficult to fully understand the true extent of PFAS pollution and its associated harms [2]. Further research could explore additional factors contributing to PFAS contamination and assess their relative impact on water quality. Seasonal fluctuations may also influence PFAS concentrations in surface and groundwater sources, with increased runoff during wet seasons or lower dilution during dry spells potentially affecting contaminant levels. Without accounting for these temporal variations, the observed differences between 2017 (measured in January) and 2023 (measured in July) may partly reflect seasonal dynamics.

The reduction in PFAS concentrations observed in our study may have important public health and economic ramifications. Lower levels of PFOA and PFOS in drinking water may decrease the population’s overall exposure to these harmful substances. Epidemiological studies have linked PFAS exposure to adverse health outcomes, including certain cancers, immune system dysfunction, and endocrine disruptors [22]. Thus, even modest reductions in PFAS levels could lead to meaningful improvements in public health, potentially reducing the burden on healthcare systems. Economically, the benefits of mitigating PFAS contamination extend beyond improved health outcomes. Obsekov et al. quantified the economic costs attributable to legacy PFAS exposures in the United States for 2018, estimating a lower bound of $5.52 billion in PFAS-related disease costs—with sensitivity analyses suggesting overall costs could be as high as $62.6 billion [23]. These figures underscore the substantial economic implications of regulatory inaction. In this way, if the legislative measures observed in our study contributed to the decline in PFAS concentrations, they offer not only environmental and health benefits but also economic advantages for Californians.

The public health and economic implications of PFAS underscore the broader societal value of robust environmental regulations. While our study focuses on the quantitative assessment of PFAS levels, understanding these downstream benefits further justifies the need for continued and enhanced policy efforts to address PFAS contamination. Building upon the findings of this research, future studies should consider several avenues for further investigation. Researchers may explore the specific mechanisms through which legislative changes influence PFAS contamination levels in drinking water. This investigation could involve in-depth analyses of compliance with MCLs, the effectiveness of monitoring efforts, and the impact of regulations on industries contributing to PFAS pollution. Additionally, it is crucial to consider identifying and regulating PFAS as a class. Currently, estimates of the number of PFAS substances vary. According to the U.S. EPA’s CompTox Chemicals Dashboard, there are nearly 15,000 recognized PFAS compounds [24]. However, other studies suggest that if a broader structural definition is applied—one that includes any chemical containing a –CF2– group—the number of PFAS could potentially approach 7 million [25]. This discrepancy, which reflects ongoing debate about what should be considered a “true” PFAS, underscores the challenges in regulating such a diverse group of chemicals and highlights the need for a unified, comprehensive approach. Furthermore, future studies should delve into the socioeconomic implications of PFAS contamination, with a particular emphasis on environmental justice communities. Examining disparities in exposure, access to clean water, and the effectiveness of remediation efforts can inform more effective and targeted policy interventions. Ultimately, our study suggests that the multifaceted approach taken by California between the pre-legislation period (2017) and post-legislation period (2023) can serve as a model for other regions facing similar challenges. By quantifying the impact of California’s legislative measures, this study demonstrates how combining contaminant thresholds, targeted financial allocations for water treatment, and product-level chemical restrictions may accelerate reductions in PFAS levels within public water systems. These results provide a rare, policy-specific benchmark for other industrialized nations considering enforceable drinking water limits and offer a practical template for countries struggling with PFAS contamination.