This document discusses the removal of heavy metals from water using nano metal oxides. It introduces heavy metals as relatively high density metals that are toxic, like lead, arsenic, cadmium and mercury. Heavy metals accumulate in organisms and can be harmful. Nano metal oxides like ZnO are effective at removing heavy metals from water through adsorption and photocatalysis mechanisms involving the absorption of light and production of electron-hole pairs on the nanoparticle surface. This allows for the reduction of heavy metals or reaction with electron acceptors. Nano metal oxides provide an efficient and low-cost approach for heavy metal removal through these photocatalytic processes.