Socio‐hydrology was introduced 4 years ago into the scientific lexicon, and elicited several reactions about the meaning and originality of the concept. However, there has also been much activity triggered by the original paper, including further commentaries that clarified the definitions, and several papers that acted on the definitions, and through these activities further clarified and illustrated the meaning and usefulness of socio‐hydrology for understanding coupled human–water systems and to assist with sustainable water management. This paper restates the case for socio‐hydrology by articulating the need to consider the two‐way feedbacks between human and water systems in order to explain puzzles, paradoxes, and unintended consequences that arise in the context of water management, and to suggest ways to avoid or overcome these challenges. The paper then presents a critical review of past research on socio‐hydrology through the prism of historical, comparative, and process socio‐hydrology, documenting both the progress made and the challenges faced. Much of the work done so far has involved studies of socio‐hydrological systems in spatially isolated domains (e.g., river basins), and phenomena that involve emergent patterns in the time domain. The modeling studies so far have involved testing hypotheses about how these temporal patterns arise. An important feature that distinguishes socio‐hydrology from other related fields is the importance of allowing human agency (e.g., socioeconomics, technology, norms, and values) to be endogenous to the systems. This paper articulates the need to extend socio‐hydrology to explore phenomena in space and in space‐time, as the world becomes increasingly globalized and human–water systems become highly interconnected. The endogenization of human agency, in terms of values and norms, technology, economics, and trade must now be extended to space and to space‐time. This is a necessity, and a challenge, for water sustainability, but presents exciting opportunities for further research.