This paper discusses the scalar politics of the water rights adjudication process in New Mexico (US). Over the past 150 years, water governance in New Mexico has gradually shifted away from communal management towards more individualised 'water rights'. This paper addresses the consequences of this shift for water users while also addressing the literature on the politics of scale and scalar politics. Actors engaged in water governance mobilise scale, and scalar politics operate in different settings, depending on the priorities of the stakeholders. Using interviews, archival research, and institutional ethnography, I illustrate how scale of various kinds is fundamental to the process of water rights adjudication and water governance in the state of New Mexico. Although the academic sense of the politics of scale remains contested, these debates seem largely abstract to most water users, even if they materially and rhetorically engage in multiple levels of scalar politics. The framing of scale arguments ranges from the biopolitics of individual water rights holders, to the new regionalisation of ditches due to adjudication, to considerations at the larger watershed level.