The litigation between the Agua Caliente Band of Cahuilla Indians and several water districts in southern California may address the unclear ownership of aquifer pore spaces directly. In this case, the tribal parties have claimed a federally reserved right to aquifer pore spaces as a component of the mineral estate of their reservation. This directly addresses whether parties may have exclusive rights to store water in an aquifer or must share storage rights with others. The resolution of this question has important implications to aquifer unitization, including defining the necessary parties to the agreement and the allocation of shares. The court has several potential methods of resolving this question, which would determine the basis of public and private rights to the use of the aquifer.

The suggested shift in policy perspective from groundwater to aquifers challenges the traditional approach to groundwater as a public resource issue. The legal issues involving aquifers are a complex combination of public rights and private property. Groundwater is traditionally a publicly held resource, yet the aquifer’s storage space appears to be considered private property. Although these resources are interconnected, courts have taken different approaches to addressing conflicts that involve indirect effects of groundwater extraction, like subsidence and subterranean trespass. Some states and courts treat pore spaces akin to a mineral right and protect private uses, like carbon sequestration. In other cases, courts have treated pore spaces as a public resource and refused claims of trespass and nuisance when adjacent aquifer uses interfered with private property rights. There is no clear consensus as to the ownership of aquifer pore spaces.