Forms a water-specific channel that provides the plasma membranes of red cells and kidney proximal tubules with high permeability to water, thereby permitting water to move in the direction of an osmotic gradient. Homotetramer (By similarity). Interacts with EPHB2; involved in endolymph production in the inner ear. Identified in a complex with STOM (By similarity). Detected in fetal kidney (at protein level). Detected in fetal kidney. Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Pharmacologically inhibited by submillimolar concentrations of mercury. Belongs to the MIP/aquaporin (TC 1.A.8) family.