The Guaraní Aquifer, locate beneath the surface of the original four Mercosur countries (Argentina, Brazil, Paraguay and Uruguay), is one of the world's largest aquifer systems and an important source of fresh water for its people. Named after the Guaraní tribe, it covers 1,200,000 km², with a volume of about 40,000 km³, a thickness of between 50 m and 800 m and a maximum depth of about 1,800 m. It is estimated to contain about 37,000 km³ of water (arguably the largest single body of groundwater in the world), with a total recharge rate of about 166 km³/year from precipitation. It is said that this vast underground reservoir could supply fresh drinking water to the world for 200 years. Due to an expected shortage of fresh water on a global scale, which environmentalists suggest will become critical in under 20 years, this important natural resource is rapidly becoming politicized, and the control of the resource becomes ever more controversial.