Water channel required to promote glycerol permeability and water transport across cell membranes (PubMed:7526388, PubMed:7517548). Acts as a glycerol transporter in skin and plays an important role in regulating SC (stratum corneum) and epidermal glycerol content. Involved in skin hydration, wound healing, and tumorigenesis. Provides kidney medullary collecting duct with high permeability to water, thereby permitting water to move in the direction of an osmotic gradient. Slightly permeable to urea and may function as a water and urea exit mechanism in antidiuresis in collecting duct cells. It may play an important role in gastrointestinal tract water transport and in glycerol metabolism (By similarity). Channel activity is inhibited by mercury ions. Detected in kidney medulla and papilla, in collecting duct cells (PubMed:7526388, PubMed:7517548). Detected in colon (PubMed:7517548). 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. Truncated N-terminus.