The idea that water-drinking is healthy took shape in medical science throughout Europe from the seventeenth century onwards. This article adds new insights to this development through a focus on the Dutch field of medicine between 1630 and 1750. It shows how a major scientific context for this shift could be found in the specific combination of Helmontian iatrochemistry and Cartesian medicine. Yet, the development of thinking about drinking water was also very much shaped by social practices and technological advances outside of medicine. Chronologically, the increased social practice of the capture of rainwater and the technological improvements of cisterns and filtration systems in the seventeenth century precede the more positive medical opinion on water in the late seventeenth and early eighteenth century. The idea that water-drinking was beneficial came into medicine through social practice, rather than the other way around. In the eighteenth century, water-drinking was seen as beneficial in the mainstream of medicine, with explicit references being made to earlier technological advances in filtration.