In arid and semi-arid regions, where water demand exceeds water availability, water security is becoming a significant concern not only related with water availability but also with rigorous and costly requirements to remove conventional and emerging contaminants from effluents discharging into drinking water sources or as water reuse becomes an alternate water supply for communities in these regions. Water and wastewater treatment demands a great amount of energy and resources, highlighting the need for novel applications of the circular economy concept. Circular Economy Applications for Water Security examines knowledge gaps, avenues of future research, and challenges related with the potential of enhanced underutilized/waste materials as transition to circular economy applications for ensuring the proper quality of water. Includes fundamental information and practical examples that helps to better understand the concepts included. The circular economy concept is helpful to incept sustainability in the water treatment processes. Every chapter will include identification of knowledge gaps, avenues for further research, and challenges that guide readers towards real state-of-the-art analysis. Contributors will be expert in their areas which will commit to explain concepts is a user-friendly way without missing scientific rigor.