Water shortages are a reality all over the world, and supplying water to urban centers is one of the challenges of modern society. This book examines the processes, uses and importance of water filtration systems. It begins with a discussion on osmosis pretreatment of seawater for thermal desalination. The following chapter reviews the Neptune Project. Chapter three demonstrates that the use of electrocoagulation coupled with microfiltration/ultrafiltration membranes is a possible technique to adjust the quality of reclaimed municipal wastewater for water reuse. Chapter four provides an evaluation of ion exchange as a pretreatment method to decrease membrane fouling. The last chapter addresses the treatment of the effluents by-produced in olive mills, generally called olive mill wastewaters.