La quantité d'eau potable dans le sous-sol africain

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00:00 The amount of drinking water in the African subsoil is estimated to be 660,000 km3.

00:06 That's a little over 100 times more than the amount of rain that falls on the surface every year.

00:13 On this continent, as elsewhere, almost everywhere in the world,

00:16 the subsoils seem to be overflowing with an almost inexhaustible amount of fresh water.

00:22 It's easy to imagine that by draining it, we can solve all the problems of access to drinking water.

00:27 But in reality, on average, only a tenth of these subsoil resources are actually exploitable.

00:34 In the Libyan desert, the rains of the highly controversial Project of Great Artificial Rivers,

00:39 which exploit the precious subsoil blue gold reserves,

00:42 are already falling to more than 400 meters deep.

00:46 And we think that at the rate at which we hit it,

00:48 in 50 years, these aquifers should be about 100 meters lower than they are today.

00:54 As gigantic as they are, these reserves, which took millennia to form,

01:00 are unfortunately not eternal.

01:02 Let's take the example of the immense Ogalala Aquifer,

01:05 which in the USA extends under the Great Plains of eight different states.

01:09 There, in a mixture of sand, lime, clay and gravel,

01:13 lies one of the most precious treasures on the North American continent.

01:17 Because Ogalala, not content with having a funny name,

01:21 provides drinking water to millions of Americans and indirectly feeds them as well.

01:27 In this satellite photo, we can see 1,400 square kilometers of fields,

01:31 which in Kansas are all flooded with water, drained into the groundwater.

01:35 Since 1950, the amount of water contained in Ogalala has been reduced by nearly 10%.

01:42 This may seem little, but already many wells have dried up,

01:45 and it is estimated that by continuing to drain at the rate at which they do so,

01:49 American farmers should see this aquifer dry, let's say, in about twenty years.

01:56 When we think about the fact that today,

01:58 nearly a third of the land irrigated by the United States is based on this aquifer,

02:03 we become aware of the importance of this invisible water.