Indirect Potable Reuse (IPR) is the blending of advanced treated, recycled or reclaimed water into a natural water source (groundwater basin or reservoir) that could be used for drinking (potable) water after further treatment.
Indirect Potable Reuse: A Sustainable Water Supply Alternative provides an overview of significant indirect potable reuse projects, followed by a description of the epidemiological and toxicological studies evaluating any potential human health impacts of these projects. A summary of key operational measures to protect human health and the areas that require further research are discussed.
The EPA website Water Recycling and Reuse: The Environmental Benefits discusses the opportunities for water recycling and the environmental benefits associated with this practice.
Examples of Indirect Potable Reuse projects include the Groundwater Replenishment System in Orange County, California (in operation since 2008) and San Diego, California's Water Purification Demonstration Project which is expected to lead to Full-Scale Reservoir Augmentation. Here's a 2013 update on the history that led to that and a news report of the San Diego City Council's 2014 approval of the project.
The treatment technologies used in IPR systems have proved to be very reliable and capable of producing water that not only meets U.S. drinking water standards, but also is often higher quality than existing water sources. Because of this, efforts are underway in California, Texas and in other states to develop guidelines and regulations for Direct Potable Reuse (DPR) of highly treated wastewater. In DPR, the treated wastewater would be piped directly into the water supply system rather than being combined with other water sources in a groundwater basin or large reservoir. Understandably, concerns exist with this type of arrangement, so the development of guidelines and regulations are necessary to ensure that the appropriate technology is used, there are redundant treatment steps, appropriate monitoring systems are used to ensure water quality, and treatment system operators are adequately trained.
In 2015 WateReuse, American Water Works Association, Water Environment Federation and National Water Research Institute released a report Framework for Direct Potable Reuse which provides a context for Direct Potable Reuse (DPR), including the costs, benefits, energy requirements, and comparative issues with other water sources and measures. Following this introduction, three key components of a DPR program are examined: (1) regulatory considerations (e.g., measures to mitigate public health risks); (2) technical issues related to the production of advanced treated water; and (3) public support and outreach. This technology is truly coming of age.
In California, an expert panel and an advisory group have been meeting to develop the necessary regulations to allow safe use of DPR, as mandated by this legislation.