Water scarcity is one of the most important and greatest challenges of the current century and effects on many critical areas for society: food, energy, security, and the environment. One of the important strategies in the free-surface reservoir is evaporation control from the water surface, which in many cases is more economical to collect and store the same amount of water from other sources. The use of nanotechnology in the water industry as one of the most important foundamental of human life and the industry has become one of the requirements of science and knowledge of the present century. Therefore, in this study, polymer coverage based on nanotechnology have been developed to prevent and reduce the evaporation of water from free-surface reservoirs. According to the purpose of this study, high-density polyethylene and zinc oxide nanoparticles were used to produce the cover. High-density polyethylene/Zinc oxide nanocomposite was produced in a complete and continuous system of micro-extruder-micro-injection by adding zinc oxide nanoparticles in 1, 5, 10 and 12 wt% to high-density polyethylene. First of all, the properties of nanocomposites were evaluated by using FE-SEM, X-ray diffraction (XRD) and Fourier transformation infrared spectroscopy (FT-IR) tests. Then, mechanical properties including tensile, flexural, thermal properties, photo-degradatio have been evaluated and finally, the anti-algae and anti-bacterial properties of nanocomposite samples and the quality of water containing to the nanocomposite samples have been investigated. According to FE-SEM results, the best homogeneous and uniform distribution and adhesion between nanoparticles and polymer matrix were obtained for nanocomposites containing 1% wt. of zinc oxide nanoparticles. By investigating the photo-degradation, the mechanical properties at 48, 96 and 240 hours were generally increased compared to the before UV exposure but in all conditions, for nanocomposites containing 1 wt% of zinc oxide, the highest increase in properties were observed. The results of the XRD and DSC tests indicate that with increasing nanoparticles, more crystals are produced with smaller sizes. In the study of anti-algae properties, the lowest levels and the anti-algae properties were observed for nanocomposites, pure polyethylene, Plexiglas, wood, and bone fiber, respectively. The results of water quality assessment indicate that all parameters of pH, electrical conductivity, nitrate, phosphate, the reached of zinc element in the water were in the standard range; only potassium content was showed outside the range of relevant standards. Finally, antibacterial properties were observed and 10 and 12 wt% of ZnO nanoparticles showed 100% antibacterial ratio for common bacteria E. coli., But for the bacteria Staphylococcus aureus and the Pseudomonas aeruginosa, the antibacterial rate decreased. Key words Prevent evaporation of water, Nanocomposite, High-density polyethylene, Zinc oxide nanoparticles, Photo-degradation, Anti-bacterial, Anti-algae