OECD cities usually benefit from high levels of protection against water risks and most city dwellers have access to reliable water services. At the same time, OECD cities face significant challenges to protect inhabitants from risks of floods, droughts or deteriorating water quality resulting mainly from urban growth, competition among water users, urban and agricultural pollution and climate change. They also face particular challenges due to ageing infrastructures and the need to adapt existing assets: most OECD cities need to transition from an era of exploiting existing infrastructures to one of building new assets and inserting such assets in existing environments.