Water permeates all realms of life and many scientific disciplines. Water problems are often taken as technical issues, subject to rationalization, optimization and best addressed by expert knowledge. Yet, in the past three decades water issues have proved to be highly divisive and have generated heated debates. Engineer-centered approaches have been challenged or paralleled by concerns for the role of social organization, institutions, power structures and, more generally, politics; economists have assumed an increasingly prominent role in stressing the significance of demand management and economic efficiency; environmentalists have been active in introducing a more holistic view of ecosystems, underlining the importance of water for the environment and human health; social activists have vied for framing access to water as a human right.