Samuel Taylor Coleridge's 18th-century Rime of the Ancient Mariner described a vast empty sea where its fictional sailors had no fresh water. Now, in the 21st century, this phrase aptly describes a spreading global water shortage.
The Earth's supply is pretty much a zero-sum game. Water covers 75% of our planet's surface. Little is added or lost; it simply is recycled. The oceans contain 97% of the world's water, and an additional 2% is tied up in the huge ice masses of the Antarctic, Arctic, and the world's glaciers. This leaves six billion people dependent on the tiny fraction of the world's water that is unfrozen and fresh.