Global Freshwater Distribution and Scarcity

Of all the water on Earth, roughly 97.5% is saline, held in the oceans, and only about 2.5% is fresh, a proportion popularized in hydrological literature through the estimates compiled by the Russian hydrologist Igor Shiklomanov and later summarized in Peter Gleick's edited volume Water in Crisis (1993). Of that small freshwater share, the overwhelming majority, on the order of 68-69%, is locked up in glaciers and permanent ice caps, chiefly the Antarctic and Greenland ice sheets, while roughly 30% exists as groundwater held in aquifers. Lakes, rivers, and other readily accessible surface water together make up less than 1% of all freshwater, and a small fraction of a percent of Earth's total water — meaning the water that sustains most direct human use, agriculture, and ecosystems is a genuinely thin slice of the planet's hydrosphere. This distribution is also profoundly uneven geographically: the Amazon basin alone discharges roughly one-fifth of the world's river flow into the ocean, while entire regions of North Africa and the Arabian Peninsula receive almost no renewable surface water at all.