Water channel required to facilitate the transport of water across membranes. Involved in osmotolerance (By similarity). Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). In microsporidia, the second signature motif differs slightly and is Asn-Pro-Gly (NPG). Belongs to the MIP/aquaporin (TC 1.A.8) family.