As a collaborative effort between EPA and USAID, this document’s primary purpose is to facilitate further development of water reuse by serving as an authoritative reference on water reuse practices. The document updates and builds on the 2004 Guidelines for Water Reuse by incorporating information on water reuse that has been developed since the 2004 document was issued. The 2012 guidelines also provide more than 100 new case studies from around the world that highlight how reuse applications can and do work in the real world.