Today membrane engineering is giving interesting solutions to some of the major problems of our modern industrialized society. Membrane bioreactors (MBR) in municipal,water treatments, membrane operations and integrated membrane systems in seawater and brackish water desalination are some important cases where membrane engineering is playing a dominant role. This manuscript discusses how membrane engineering contributes to the solution of this water problem. It gives also a vision on the current and future developments of membrane operations in the field of water treatment.