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.