Harvesting solar energy through usage of flat plate solar water collector (FPSWCs) has been widely used in different domestic, agricultural, and industrial applications. Phase change materials (PCMs), due to their unique thermo-physical properties, have been exploited in different designs of solar collectors to maximize the useful heat gained by collectors. Moreover, adding nanoparticles to PCMs to produce nanocomposite (NC) PCMs with superior thermo-physical properties added new advantages to the applications of these materials in solar collector applications. This literature review focuses on the different developments of these materials and their implementation with flat plate solar water collectors. Furthermore, the effect of adding different types of nanoparticles, including: metal, metal oxides, carbon nanoparticles, a high thermal conductivity skeleton graphite, and metal foams, on the heat transfer behavior and thermal conductivity of PCMs are also reviewed and analyzed. The reviewed results indicated that a significant improvement in the thermal conductivity of PCMs has been obtained using carbon-based nanoparticles, specifically graphite and graphene nano-platelets compared to metal and metal oxides nanoparticles at different nanoparticle concentrations. It is also revealed that, the integration of the PCMs in FPSWCs leads to a satisfactory storage capacity and could provide hot water temperature for a longer time. Moreover, it is recommended that the use of NCPCMs may be considered as an effective tool to improve the efficiency of the FPSWC. However, further optimization studies are needed to explore the impact of different factors such as nanoparticle type, nanoparticle weight fraction, nanoparticle size, and PCM type on the collector performance. A noteworthy observations, important proportionalities, and future trends are also discussed. (C) 2019 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.