Sustainable development is interpreted differently by different actors. Each interpretation is at the same time scientific and ideological. A specific paradigm such as mainstream neoclassical economics is science but at the same time ideology. Neoclassical economics is not compatible with a radical interpretation of sustainable development. Water management cannot be reduced to a technical matter. The way different actors refer to theories of science, paradigms in eonomics and ideological orientations have also to be investigated. Politics enters into economics and options with respect to ideological orientation have to be discussed.