In recent years, polymer nanocomposites (PNCs) have attracted the attention of scientists and technologists in water purification due to improved processability, surface area, stability, tunable properties, and cost effectiveness. PNCs showed fast decontamination ability with high selectivity to remove various pollutants. This review provides up-to-date information about the importance of PNCs in the removal of metal ions, dyes, and microorganism from polluted water. The general methodology for preparation and properties of nanocomposites with reference to PNCs is given. Different adsorption isotherm and kinetic models along with thermodynamic parameters for adsorption have been discussed.