A nanoadsorbent based filter is used for purification of fluoride and arsenic contaminated water. 140-150 g low cost (˜10 USD/kg) nanoparticles of gamma alumina of 20-25 mg/g fluoride and 25-30 mg/g arsenic adsorption capacity is incorporated in propylene filter without susceptibility of leaching incorporated nanoparticles in water. The cost of domestic defluoridation device containing low cost nanoalumina incorporated filters/cartridges along with housing, overhead tank, tubing and treated water storage container etc. is of very low cost of around 25 USD/device. The fluoride treatment cost would be