Forms a water-specific channel; mercury-sensitive. Not permeable to glycerol or urea. Detected in the sperm midpiece (at protein level) (PubMed:28042826). Expressed only in pancreas and colon. 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.