This chapter explores changes in the way we have thought about and managed water supply. From a contemporary perspective, provision of a piped urban water supply is a crucial marker of development and modernisation. In the 1500s, London was the most developed city in the UK, with 120,000 residents. London’s contemporary water system is the legacy of that which has developed in the past. The piped water supply is the universal source of household water and the source for most commercial users of water. Thames Water currently supplies about 2,500 million litres of clean water per day (Ml/d). Pressures on Thames Water’s water supply system result from a combination of what they see as ‘demand’ and ‘supply’ factors. Demand, incorporating household use, commercial use and leakage, is expected to increase by about 10 per cent, or 250Ml/d. Depending on status and household infrastructure, for sixteenth-century Londoners ‘we’ might operate at a household, neighbourhood, ward, parish or London-wide level.