Abstract: 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 $TiO_{2}$, 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 $TiO_{2}$ for water treatment. The strategies to improve its efficiency and to enhance its photocatalytic 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 recovery, necessary to avoid their impact on the environment and human health. For this reason, the immobilization of photocatalysts on different substrates has been drawing a significant attention. Considering the various substrates, polymers seem to be very promising. The most recent developments in the applications of polymer-$TiO_{2}$ nanocomposites for water purification are presented. Finally, the recent interest addressed to the use of molecularly imprinted polymers for wastewater treatment is discussed, showing preliminary results and future perspectives.