Sand and gravel have been used to purify water for thousands of years, and in 1804, a Scotsman named John Gibb designed and built the first filter that strained water through grains of sand to remove bigger particles of contamination. His technology worked so well that pretty soon, London and other big cities in Europe were using it to make river water look clearer and taste better.
By the late 1800s, scientists figured out that filtering made water safer to drink as well, since the particles stopped by the filtering were the ones that helped to transmit the microbes that caused water-borne diseases. The value of filtering was demonstrated in 1892, when the city of Hamburg, which got its drinking water from the River Elbe, suffered a cholera epidemic that killed 7,500 people, while the neighboring city of Altona, where water from the same river was filtered, escaped almost untouched [source: Huisman and Wood].
But recently, researchers have figured out how to coat sand grains with graphite oxide to create "super sand" that reportedly can filter harmful substances such as mercury from water five times as effectively as ordinary sand. Workcontinues to find ways to make super sand absorb even more contamination, and eventually use it in developing countries where water supplies are dangerously polluted [source: Science Daily].