This paper shows that winds of change are blowing in the dry zones of north-central Sri Lanka, the original hydraulic civilisation of the world. The social organisation of tank irrigation - which for centuries had combined a stylised land-use pattern, a system of highly differentiated property rights, and elaborate rules of community management of tank irrigation - has now been morphing in response to demographic pressures, market signals, technical change and modernisation. What are the lessons for south Asia and sub-Saharan Africa?