Water in space: The water world of ISO

In this review we present the main results obtained by the ISO satellite on the abundance and spatial distribution of water vapor in the direction of molecular clouds, evolved stars, galaxies, and in the bodies of our Solar System. We also discuss the modeling of H2O and the difficulties found in the interpretation of the data, the need of collisional rates and the perspectives that future high angular and high spectral resolution observations of H2O with the Herschel Space Observatory will open.