Nationwide Assessment of De Facto Wastewater Reuse Reveals Vulnerable Drinking Water Systems and Infrastructure Gaps

Unplanned wastewater reuse, or de facto reuse (DFR), improves surface water supply resiliency but can introduce nutrients and emerging contaminants into drinking water sources. Previous national DFR assessments excluded thousands of smaller drinking water systems that serve ≤10,000 people. By expanding the De Facto Reuse Incidence in our Nation’s Consumable Supply (DRINCS) model into DRINCS2.0 to include all 6,881 U.S. surface water intakes serving ∼232 million people, we identify a previously unrecognized national infrastructure gap. DRINCS2.0 uses updated high-resolution hydrography data and post-2020 water and wastewater facility details. Although large systems serving >10,000 people experience higher DFR frequency (41% versus 34%) and magnitude (medians of 2.0% versus 1.2%), 71% of impacted small systems (≤10,000 people) lack advanced treatment (i.e., activated carbon, ozone, and reverse osmosis) capable of treating pollutants of wastewater origin, compared with 43% of large systems. Higher DFR was associated with increased PFAS occurrence in treated drinking water obtained from EPA UCMR5 data sets. Sociodemographic analysis further showed that populations with greater socioeconomic vulnerability were more likely to receive drinking water from systems impacted by DFR without advanced treatment. This study provides the most comprehensive national assessment of DFR to date and offers a screening framework to prioritize monitoring and treatment upgrades for emerging contaminants.