Direct potable reuse (DPR) involves processes where “purified municipal wastewater is introduced into a water treatment plant intake or directly into the water distribution system.”1 As populations increase and treatment technologies improve, direct potable reuse may become an economically viable or even preferred option to meet growing global water demand.
Water reuse takes many forms. Nonpotable reuse uses recycled water to supply agriculture, landscape irrigation, and industrial applications. Potable reuse, though, can be either direct or indirect. With Indirect Potable Reuse (IPR), treated wastewater passes through a buffer such as a wetland before being re-introduced to a water supply. In contrast, DPR treats wastewater far beyond typical standards for eventual direct introduction to municipal systems. This is important, as many opposing parties are skeptical of DPR and the high level of treatment that water supplies undergo. In actuality, the re-introduced water is treated to much higher quality standards. The treated water is usually stored and monitored for quality in an Engineered Storage Buffer (ESB), which might be a large controlled tank or other reservoir. While IPR has been preferred in the past, demographic, economic, and engineering factors make DPR more feasible for future use.2
DPR can provide several potential benefits. DPR maximizes use of local sources, which leaves more water for environmental and food production.1 It also can reduce energy use involved in transporting water.3 Finally, DPR maximizes investment in treatment technologies by limiting the exposure of treated water to potential contaminants in ecosystems or existing infrastructure.
Widespread implementation of DPR in municipal systems also poses many challenges. First, current infrastructure systems are not designed to handle strict DPR requirements. DPR projects require infrastructure and treatment beyond conventional systems in order to assure strict quality standards. For instance, Engineered Storage Buffers (ESBs) can facilitate storage and monitoring of treated water, but must incorporate improved monitoring techniques to meet reliability and manageable costs. Second, many small community water systems are not capable of meeting water quality requirements for contaminants such as arsenic, let alone possessing the ability for high-level treatment. Third, public opinion is skeptical and many people are simply opposed to direct reuse without sending it through a environmental or “natural” buffer.4 Environmental buffers may actually degrade the quality of highly-treated water by introducing soil and water contaminants, which increases subsequent treatment needs. Fourth, DPR necessitates management changes such as new monitoring capabilities and blending requirements. Management institutions, however, are often slow to respond to such needs for innovation due to factors of culture and finance.
DPR applications are likely to increase, especially in cities in arid climates. Nevertheless, infrastructure development, monitoring requirements, environmental quality concerns, and social norms make DPR a challenging engineering and political task. Improvements in technology, along with changes in public attitudes, are necessary to develop and implement future DPR systems.
1. Schroeder, E., Tchobanglous, G., Leverenz, H. & Asano, T. Direct Potable Reuse: Benefits for Public Water Supplies, Agriculture, the Environment, and Energy Conservation. (Prepared for the National Water Research Institute: Fountain Valley, CA, 2012).
2. Leverenz, H. L., Tchobanoglous, G. & Asano, T. Direct potable reuse: a future imperative. Journal of Water Reuse and Desalination 1, 2 (2011).
3. California Energy Commission Final Staff Report, California’s Water-Energy Relationship. (2005).
4. Lohman, L. C. Potable wastewater reuse can win public support. Proceedings of Water Reuse Symposium IV 1029–1046 (1988).