Kirin Emlet Furst

New drinking-water regulations for per- and polyfluoroalkyl substances (PFAS) are forcing utilities operating in interconnected urban “One Water” systems to make strategic choices between short-term compliance measures and more transformative interventions with long-term sustainability benefits. To examine how utilities navigate this trade-off, we worked with practitioners in the Occoquan Reservoir system (USA) to define and evaluate 57 interventions spanning drinking-water treatment, wastewater management and watershed source control. Preferred near-term strategies centered on mature treatment technologies, whereas longer-term options included advanced treatment adoption, source-control measures, regulatory actions, raw-water blending and adaptive treatment operations. The final intervention portfolio distributes action, cost and risk across multiple components of the One Water system, illustrating how regulatory pressure can catalyze sustainable pathways for PFAS management.

Disinfection of drinking water provides essential protection against microbial pathogens. However, disinfectants react with organic matter and other constituents in water to form disinfection byproducts (DBPs), which are of concern for human health. Chlorocyanurates are chlorine-based disinfectants that have been used for drinking water in point-of-use and emergency contexts. Little is known about chlorocyanurate DBP formation beyond the potential to form lower regulated trihalomethanes and haloacetic acids compared to chlorine. In this study, regulated and unregulated DBP formation was evaluated for multiple chlorocyanurate formulations to understand the effect of the chlorine-to-cyanuric acid ratio on DBP mixture composition and calculated toxicity by comparison to conventional chlorine. Chlorocyanurates produced lower regulated DBPs by ∼10-50% compared to chlorine but promoted bromine incorporation in most DBP classes by 50-200% and produced higher calculated toxicity than chlorine under most conditions. Enhanced dichloroacetonitrile formation by chlorocyanurates was partly attributed to trichloramine formation from the degradation of chlorocyanurates by hypochlorite. Thus, chlorocyanurates may promote multiple DBP toxicity drivers. Water quality and operational considerations are identified to minimize DBP toxicity while using chlorocyanurate disinfectants, which remain an important option for drinking water disinfection in low-resource settings.

Drinking water regulations often use indicators to represent risk associated with broader contaminant groups. To evaluate the efficacy of indicators, a quantitative approach is needed that aligns with the regulatory framework, in which a benchmark value represents an unacceptably high level of a contaminant or contaminant class. This policy microsimulation study develops such an approach in the context of potential regulatory revisions to address brominated HAAs, a class of disinfection byproducts. Likely scenarios include a limit on the sum of nine brominated and chlorinated HAAs (HAA9), on bromide, or on the sum of six brominated HAAs (HAA6Br). The probability of each potential regulatory indicator co-occurring with a high level of HAA6Br was quantified using logistic models. The HAA9 and bromide indicators both performed poorly, with no better than a ∼1 in 4 chance of identifying equivalently high levels of HAA6Br. Furthermore, high false positive rates (>75%) would implicate a substantial number of water systems that do not have high HAA6Br levels. This study reveals the trade-off implicit in the use of regulatory indicators, in which precision (fewer false positives) must be sacrificed to achieve greater coverage (more true positives). The methodology and findings have broad implications for evaluating indicator classes in drinking water policy and research.

Watersheds with relatively higher concentrations of disinfection by-product (DBP) precursors are of concern for public water systems (PWSs) seeking to control DBP exposure risk. In this study, the occurrence of bromide and total organic carbon (TOC), which are important DBP precursors, was evaluated in PWS source waters on a watershed basis at the hydrologic unit code 2 (HUC2) level. Variations were examined across source water type (e.g., surface water or groundwater) and watershed, and temporally based on seasonality as well as differences between the late 1990s and the years 2018–2020. The median bromide concentrations were higher in groundwater systems compared with surface water (by 25 μg/L), whereas the median TOC concentrations were higher in surface water systems compared with groundwater (by 1.7 mg/L). Surface water sources in multiple midwestern and western watersheds had a combination of elevated bromide and TOC (relative to median values of 21 μg/L and 2.5 mg/L, respectively), which was especially pronounced in the Texas-Gulf and Rio Grande watersheds. None of the HUC2 watersheds had elevated levels of both bromide and TOC in groundwater sources (median values of 50 μg/L and 1.0 mg/L, respectively). Source water bromide median watershed concentrations for very large systems were ∼20% lower in 2018–2020 than in 1998, however, more than 40% higher at the 90th percentile, whereas source water TOC median watershed concentrations for very large systems were ∼25% higher in 2018–2020 than in 1998 but less than 10% higher at the 90th percentile. These temporal differences may be related to the influence of climate change and other anthropogenic effects. In addition, many individual PWSs showed substantial change in bromide and TOC concentrations between those time periods. For example, about 7% of the PWSs had at least double the bromide concentrations, and 5% at least double the TOC concentrations, in 2018–2020 than in 1998.