For decades, communities have been reusing valuable reclaimed water to recharge groundwater aquifers, irrigate landscapes and agricultural fields, provide critical stream flows, and provide industries and facilities with an alternative to potable water for a range of uses. While water reuse is not new, population increases and land use changes, combined with changes in the intensity and dynamics of local climatic weather patterns, have exacerbated water supply challenges in many areas of the world. Furthermore, treated wastewater is increasingly being seen as a resource rather than simply 'waste.' In this context, water reclamation and reuse have taken on increased importance in the water supply of communities in the United States and around the world in order to achieve efficient resource use, ensure protection of environmental and human health, and improve water management. Strict effluent discharge limits have spurred effective and reliable improvements in treatment technologies. Along with a growing interest in more sustainable water supplies, these improvements have led an increasing number of communities to use reclaimed water as an alternative source to conventional water supplies for a range of applications. In some areas of the United States, water reuse and dual water systems for distribution of reclaimed water for nonpotable uses have become fully integrated into local water supplies. Alternative and efficient water supply options, including reclaimed water, are necessary components of holistic and sustainable water management. 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. In the United States, water reuse regulation is primarily under the jurisdiction of states, tribal nations, and territories. This document includes an updated overview of regulations or guidelines addressing water reuse that are promulgated by these authorities. Regulations vary from state to state, and some states have yet to develop water reuse guidelines or regulations. This document meets a critical need: it informs and supplements state regulations and guidelines by providing technical information and outlining key implementation considerations. It also presents frameworks should states, tribes, or other authorities decide to develop new regulations or guidelines. This 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. This document includes updated discussion of regional variations of water reuse in the United States, advances in wastewater treatment technologies relevant to reuse, best practices for involving communities in planning projects, international water reuse practices, and factors that will allow expansion of safe and sustainable water reuse throughout the world. 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.