This book represents the outcome of the Second IWA Leading-Edge Conference held in Sydney, Australia in November 2004. Sustainability is a paradoxical concept. We know we want to protect the environment from human-induced change, yet ecosystems are dynamic, constantly changing and adapting in response to a multitude of factors, the combined effect and subtleties of which are probably well beyond human calculation. Furthermore, our conscious desire to protect the environment - which forces us to think of humans as sitting outside ecosystems - conflicts with the unavoidable fact that we are an...