Seven billion humans on Earth and one in three people suffering from a lack of fresh water... Tomorrow, it will be one in two... Faced with this dramatic observation, there are solutions, including that of Alain Gachet. 96% of fresh water reserves are underground, and the geophysicist explorer has understood this well. After 20 years as an oil prospector, he abandoned black gold for blue gold. Alain Gachet, combining his skills in geology and satellite images, then developed a revolutionary system. An algorithm allows him to identify places where immense reserves of drinking water (aquifers) could be found right under the feet of populations dying of thirst. The discovery of aquifers turns out to be a major geopolitical issue, particularly in conflict zones. What role will the modern-day water diviner play in the great battle for water?