Forms a water-specific channel (By similarity). Plays an important role in fluid secretion in salivary glands. Required for TRPV4 activation by hypotonicity. Together with TRPV4, controls regulatory volume decrease in salivary epithelial cells. Seems to play a redundant role in water transport in the eye, lung and in sweat glands (By similarity). Homotetramer. Interacts with TRPV4; the interaction is probably indirect and regulates TRPV4 activation by hypotonicity. Hypotonicity increases location at the cell membrane. Phosphorylation decreases location at the cell membrane. Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Belongs to the MIP/aquaporin (TC 1.A.8) family.