Encyclopaedia Britannica reports that “the Antarctic Ice Sheet has a volume of 28 million cubic km (about 6.7 million cubic miles), which represents 70 percent of the total fresh water (including groundwater) in the world.” Seven-tenths of the planet’s fresh water sits in a single ice sheet at the bottom of the world.
The temptation is to read that as reassuring. A planet with that much fresh water in reserve sounds like a planet with a comfortable margin. That’s not quite the case.
Where the fresh water actually sits
Look beyond Antarctica and the rest of the picture follows the same pattern. By one widely cited estimate, the U.S. Geological Survey reports that “the majority of total freshwater on Earth, about 68.7 percent, is held in ice caps and glaciers.” More than two-thirds of the planet’s fresh water is frozen solid.
That ice is not evenly distributed. The USGS notes that almost 90 percent of Earth’s ice mass sits in Antarctica, with roughly 10 percent in the Greenland ice cap and a sliver in mountain glaciers. The National Snow and Ice Data Center gives the Antarctic sheet an area of almost 14 million square kilometres and a volume nearer 30 million cubic km. The two bodies agree on the shape of it: one ice sheet at the bottom of the world holds something close to seven-tenths of all the fresh water there is.
Why “fresh water” is a misleading comfort
Existing and being reachable are not the same thing, and almost all of that frozen water fails the second test. It is locked in ice at the poles, kilometres thick in places, far from anywhere people live and frozen at temperatures that make extraction a big engineering problem. The largest freshwater reservoir on Earth is also the one least available to us.
Subtract the ice and what remains is still mostly out of reach. Roughly 30 percent of fresh water is groundwater, and much of it sits too deep to pump at any practical cost. The sliver left over is the part that actually keeps people alive. The National Geographic Society puts it plainly: “That leaves only about one percent of Earth’s fresh water as readily available for human use.” The U.S. EPA frames the same point for the public: “The Earth might seem like it has abundant water, but in fact less than 1 percent is available for human use.”
Those percentages describe different slices of the budget and should not be lined up as rivals. The 68.7 percent is a share of all fresh water. The one percent is the share that is both fresh and easy to reach. Together they sketch the same uncomfortable picture.
The gap between existing and accessible
None of this means the planet is running dry, and the figures call for clarity more than alarm. The total freshwater stock is enormous. The reachable portion is tiny, and it does not grow because the ice sheet does. Water security is a problem of access and distribution, not of global supply, which is why a continent of frozen fresh water offers no help to a city in drought.
