Nanotechnology offers the potential of novel nanomaterials for the treatment of surface water, groundwater, wastewater, and other environmental materials contaminated by toxic metal ions, organic and inorganic solutes, and microorganisms. Due to the unique activity toward recalcitrant contaminants, nano photocatalyst has great potential for use in the treatment of water and contaminated sites. The present market of nano photocatalyst based technologies known as the nano water treatment are applicable to not only wastewater but also drinking water. Nanotechnology is expected to deal more efficiently with contaminants that conventional water treatment systems struggle to treat, including bacteria, viruses, high-toxic organic matter and heavy metals. This efficiency generally stems from the very high specific surface area of nanomaterials, which increases dissolution, reactivity and sorption of contaminants. Photocatalytic oxidation technology could be an ultimate purification technology for water, not just simply filter the water, it does purify the water indeed. With a nano water treatment, organic and harmful contaminants will be destroyed and converted to harmless inorganic end products, e.g. water, carbon dioxide, inorganic ions. It can be used to remediate the environmental water system, so called the nanoremediation, which has been most widely used for groundwater treatment, with additional extensive research in wastewater treatment.