Aquaporins form homotetrameric transmembrane channels, with each monomer independently mediating water transport across the plasma membrane along its osmotic gradient (PubMed:18768791, PubMed:8621489). Plays an important role in fluid secretion in salivary glands (By similarity). Required for TRPV4 activation by hypotonicity. Together with TRPV4, controls regulatory volume decrease in salivary epithelial cells (PubMed:16571723). Seems to play a redundant role in water transport in the eye, lung and in sweat glands (By similarity). {ECO:0000250|UniProtKB:Q9WTY4, ECO:0000269|PubMed:16571723, ECO:0000269|PubMed:18768791, ECO:0000269|PubMed:8621489}. This is the function of Ensembl gene identifier ENSG00000161798 (AQP5, aquaporin 5).