The World Health Organization (WHO) estimated that 80% of illnesses in the developing world are water related. More than million people die every year from diseases caused by bacterial infection due to the poor quality of drinking water. Even in developed countries, water supply has become a serious issue due to the climate change and increasing natural disasters. Nanotechnology is expected to have the potential to address this important global challenge. For example, nano-scale photocatalysts are useful for decomposition of organic pollutants and microorganisms, by using sunlight as a renewable energy source. Nanoscale redox-catalysts can effectively reduce the toxicity of heavy-metal ions. This project aims to develop novel nano-photocatalysts and nano-redox-catalysts to ensure our water security.