For more than thirty years, for Sebastiao Salgado, photography has been a weapon. Honest and uncompromising, the visual writing of the most famous photojournalist is unique. A question of perspective: his respects and celebrates human dignity, in its tragedies as in its joys. His optimism, tempered with lucidity, and his militant generosity force us to question the future of our planet. As an international decade of action dedicated to water opens this year, under the aegis of the United Nations, the Brazilian photographer shows us here, with all the clarity of the evidence, how much it, of all our resources, is the most precious, and the most threatened.