Abstract: Evaporation is the most important hydrological function on Earth because it provides rain. As deforestation and urbanisation reduce plant cover and evapotranspiration, ever more short-wave solar radiation is converted to long-wave thermal emissions and sensible heat. Higher surface temperatures set up heat island effects, contributing to local, and ultimately, global climate change. Rainwater harvesting is therefore a key mitigation strategy against increased temperatures and drought. Urban water management can be enhanced by the ecological design of green roofs, evaporative facades, and ground infiltration measures, and in Berlin, several such projects are demonstrating these New Water Paradigm principles in action.