Forms a water-specific channel that provides the plasma membranes of renal collecting duct with high permeability to water, thereby permitting water to move in the direction of an osmotic gradient (PubMed:15509592, PubMed:7510718, PubMed:7524315, PubMed:8140421, PubMed:8584435). Plays an essential role in renal water homeostasis (PubMed:15509592, PubMed:7524315, PubMed:8140421). Could also be permeable to glycerol (PubMed:8584435). {ECO:0000269|PubMed:15509592, ECO:0000269|PubMed:7510718, ECO:0000269|PubMed:7524315, ECO:0000269|PubMed:8140421, ECO:0000269|PubMed:8584435}. This is the function of AQP2 (aquaporin 2, Ensembl gene identifier ENSG00000167580).