Photo-catalysis is one of the most explored phenomenons to obtain potable water in remote areas. The term “photo-catalysis” is understood as a chemical reaction which is caused by photo-absorption of a matter also known as “photo-catalyst”, which remains unaltered throughout the reaction. In this process, water molecules adsorbed over the surface of photo-catalysts in normal environments are used to participate in the reaction to decompose pollutants in water. Since the photo-catalytic reactions are possible in air, the oxygen reduction is the significant phenomenon in photo-catalytic reduction. This chapter aims to cover the fundamental aspect of photo-catalytic phenomenon and its significant role in water purification. Explicit examples on the amalgamation of photo-catalysis and various photo-catalytic set-ups developed are also illustrated. © 2018, Springer Nature Singapore Pte Ltd.