This Environmental briefing produced by Spinverse Oy and Empa outlines the social and economical relevance of nano-enabled photocatalysis, provides background information on the technology, and highlights further challenges to be addressed. The summary was produced for the ObservatoryNANO project, which is funded under FP7. The challenges in treating waste- and drinking water are dependent on the origin of the water. Problematic substances in wastewater can include organic matter and/or different trace contaminants. Industrial wastewater may additionally contain heavy loads of metals or organic compounds. In drinking water production microbe contamination needs to be addressed especially in developing countries, but also for remote locations without access to a centralized drinking water supply.