There is, it is often observed, no waste in nature; waste comes from culture. This means that if there were no human-generated material flows – water, energy, phosphorus, nitrogen, food, carbon dioxide and so on – there would be no waste. But it does not follow from this that the more human-generated flows there are, the more waste there will be. By re-engineering our cities’ infrastructures in ways that enjoy the consent of their citizens – our focus in this paper is on water and its conversion into wastewater – we can progressively alter the material flows from ‘bad’ to ‘good’, with the ultimate goal of making those cities into forces for good in the environment.