Water was essential to the commerce, sustenance and cleansing of medieval London and its inhabitants. The paper reviews technologies of supply, access and control, and the uses and risks associated with water during the city's formative period. It surveys the pleasures of water around the city, the paradoxes they involved, and the public supply as an expression of a growing civic culture. It emphasizes the interaction between natural environment, technology and institutions as a fruitful theme for medieval urban history.