Water in the interstellar medium of galaxies

Water is a key constituent of interstellar matter, with a great influence on the formation of stars, planets, and life.The rotational and vibrational transitions of H2O are useful tracers of physical and chemical conditions in a broad range of astrophysical objects.This talk reviews recent observations of water in Galactic interstellar clouds and star-forming regions, as well as nearby galaxies and distant starbursts and AGN.Results are presented from several Herschel key programs, and prospects are outlined for future observations with ALMA and beyond