The culturally rooted conception that water is a free good does not acknowledge that it is a common-pool resource, which, in the case of Argentina, it is public property. In this paper we review the classical theories and some contemporary approaches to the question of ground rent to apply this concept to the use of groundwater by farmers and seed companies in the north of the province of Buenos Aires. Based on this case study, we argue that the use of water for irrigation, as a non-produced means of production, implies, through the absence of effective regulation, the appropriation of a territorial rent. To understand its existence and appropriation, it is necessary to consider the differences between water and land resources. In conclusion we claim the existence of water rent as a particular type of rent in the irrigated agriculture of agrarian capitalism.