Water is essential for life on Earth, and liquid water must have plaid a major role in the apparition and development of life on Earth. But water is not present only on Earth : in the form of vapor or ice, it has been found everywhere in the Universe, from the most distant galaxies to the nearby planets.
Our knowledge of solar-system bodies has made a huge progress over the past decades, mostly driven by the space exploration of the Moon and planets. In spite of many still open questions, we now have a good understanding of how the solar system formed. In particular, it appears that water has plaid an essential role, both in the formation of the planets (making the two classes of planets, telluric and giant), and in the evolution of the terrestrial planets (leading to diverging destinies for Venus, the Earth and Mars). Water is also the essential constituent of solid bodies in the outer solar system (comets, rings and outer satellites).
In this talk, we will discuss the role of water in the solar system history, using in particular recent results obtained by space missions (Mars Express on Mars, Cassini-Huygens on Saturn and Titan). In conclusion, as a possible tool in the quest for life outside the solar system, we will address the question of searching for water in extrasolar terrestrial planets, if such exoplanets are found in the future.