Nanomaterials show a better performance in environmental remediation than other conventional materials because of their high surface area and their associated high reactivity. Nanostructured photocatalysts, especially TiO2, are widely studied for the treatment of contaminated water. They can indeed degrade organic pollutants and microorganisms. In the first part of this review, the fundamentals of heterogeneous photocatalysis are described, with particular attention to the most important recent progresses in the field of nanostructured TiO2 for water treatment. The strategies to improve its efficiency and to enhance its photo-catalytic performance in the visible region are also illustrated. However, although the nanoscaled catalysts show considerable improvement in terms of water purification efficiency, their size remains the main problem in a large-scale process because of the need of a post-treatment …