portunities to expand nonpotable water reuse because it is more cost-effective to install separate nonpotable water distribution systems at the same time the primary drinking water distribution system is installed. In existing communities nonpotable water reuse is often restricted by the high costs associated with constructing the distribution system and retrofitting existing plumbing (see also Chapter 9).

The use of reclaimed water to augment potable water supplies has significant potential for helping to meet the nation’s future needs, but potable water reuse projects only account for a relatively small fraction of the volume of water currently being reused. However, potable reuse becomes more significant to the nation’s current water supply portfolio if de facto or unplanned water reuse is included. The de facto reuse of wastewater effluent as a water supply is common in many of the nation’s water systems, with some drinking water treatment plants using waters from which a large fraction originated as wastewater effluent from upstream communities, especially under low-flow conditions.

An analysis of the extent of de facto potable water reuse should be conducted to quantify the number of people currently exposed to wastewater contaminants and their likely concentrations. Despite the growing importance of de facto reuse, a systematic analysis of the extent of effluent contributions to potable water supplies has not been made in the United States for over 30 years. Available tools and data sources maintained by federal agencies would enable this to be done with better precision, and such an analysis would help water resource planners and public health agencies understand the extent and importance of de facto water reuse. Furthermore, an analysis of de facto potable reuse may spur the additional development of contaminant prediction tools and improved site-specific monitoring programs for the betterment of public health. USGS and EPA have the necessary data and expertise to conduct this analysis on large watersheds that serve as water supplies for multiple states. For smaller watersheds or watersheds with existing monitoring networks, state and local agencies may have additional data to contribute to these analyses.

Environmental buffers can play an important role in improving water quality and ensuring public acceptance of potable water reuse projects, but the historical distinction between direct and indirect water reuse is not meaningful to the assessment of the quality of water delivered to consumers. Potable reuse projects built in the United States between 1960 and 2010 employed environmental buffers in response to concerns about public health risks and the possibility of adverse public reaction to potable water reuse. In the last few years, a potable reuse project was built and another is being built without environmental buffers, and the trend toward operating potable reuse projects without buffers is likely to continue in the future. An environmental buffer should be considered as one of several design features that can be used to ensure safe and reliable operation of potable reuse systems. As a result, they need to be designed, evaluated, and monitored like other elements of the water treatment and delivery system. See Chapters 4 and 5 for additional details on the treatment effectiveness of environmental buffers and their role in quality assurance.

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