The Amazonas Aquifer, the largest known in the world, is a strategic reserve of potable water, say Brazilian authorities. Also known as Alter do Chão, for the geological formation where it is located, has an area of about four million square kilometers, three times the also gigantic Guaraní Aquifer, which Brazil shares with Argentina, Paraguay and Uruguay.

The Amazonas Aquifer extends from the mouth of the Amazon River “to the foothills of the Andes,” Marco Oliveira, local superintendent of the National Geological Service, told Tierramérica.

The existence of the aquifer has long been known – it is a common trait of sedimentary river basins – but “only now do we have the data that prove its size,” Oliveira said. It is not yet known how far it extends into the neighboring countries.

The aquifer's water – potable and purer than surface waters – already supplies a good portion of the Amazon population, including 30 percent of the 1.8 million residents of Manaus, capital of Amazonas state. The aquifer is also a safeguard against potential catastrophes that would contaminate the rivers, said Oliveira.