Abstract. This paper traces the development and eventual recognition of hydrology as a scientific subject in its own right in the UK and, later, in the European Geophysical Society (EGS), now the European Geosciences Union (EGU). In the early 1960s, to facilitate decisions of executive government departments in meeting the rapidly increasing demand for industrial and domestic water supplies, a small Hydrological Research Unit (HRU) was established by the UK Department of Scientific and Industrial Research(DSIR) to investigate the comparative water use of forested and grassed upland catchments. These small beginnings in the HRU developed in a few years into the highly multi-disciplinary Institute of Hydrology (IH) as a source of independent advice for policy makers, with a capability to undertake longer term research, monitoring and data collection than was feasible in individual government departments or in the universities. Within IH, the range of specialities included not only engineering, physics, geography, geology, meteorology and instrumentation but also pollution, plant physiology, ecology, chemistry and economics. Said quickly in retrospect, the trajectory of the growth of IH seems smooth but, in reality, it masked many struggles between competing disciplines and departments before hydrology was recognised as a subject in its own right – the science of water.