Addressing the Contribution of Indirect Potable Reuse to Inland Freshwater Salinization

Inland freshwater salinity is on the rise in many regions across the globe—a phenomenon called the freshwater salinization syndrome (FSS). In this paper we investigate a potential conflict between managing the FSS and indirect potable reuse, the practice of augmenting water supplies through the addition of reclaimed wastewater to surface waters and groundwaters. From time-series data collected over the past 25 years, we quantify the contributions of three salinity sources—a wastewater reclamation facility and two rapidly urbanizing watersheds—to the rising concentration of sodium (a major ion associated with the FSS) in a regionally important drinking water reservoir in the Mid-Atlantic United States. Sodium mass loading to the reservoir is primarily from watershed runoff during wet weather periods and reclaimed wastewater during dry weather periods. Across all timescales evaluated, sodium concentration in the reclaimed wastewater is higher than in outflow from the two watersheds. Sodium in reclaimed wastewater originates from chemicals added during wastewater treatment, industrial and commercial discharges, human excretion, and down drain disposal of drinking water and sodium-rich household products. Thus, numerous opportunities exist to reduce the contribution of indirect potable reuse to sodium pollution at this site, and the FSS more generally. On the ground implementation will require deliberative engagement with a diverse community of watershed stakeholders and careful consideration of the local political, social, and environmental context.