Recent work and publications concerning sustainable water stewardship in Raja-sthan (India) highlight how contemporary challenges are eroding traditional, communal approaches to water stewardship through mechanised extraction be-yond the renewable capacities of ecosystems. Our work is focused on developing a formal ontology for modelling the knowledge of traditional water stewardship in India’s drylands by capturing the key constitutional elements of regenerative methods. Our method follows an iterative evolving prototype process for deliver-ing the first version of the Ontology for Sustainable Water Stewardship (WASOS). The ontology contains a moderate number of high-level classes and properties that represent the water management decision-making process. By making key relationships visible, we aim to support decision-making in complex catchments particularly where there are contested urban and rural claims on water.