aquifer

Aquifer is a modern coinage from Latin aqua (water) and ferre (to bear, carry). The word was assembled by geologists in the nineteenth century to name underground layers of rock, sand, or gravel that hold and transmit water. An aquifer is not an underground river — though that image persists — but a porous geological formation saturated with water. The water fills the spaces between grains of sand or cracks in rock. The aquifer carries water the way a sponge carries water: by holding it in its structure.

The concept was not new. Ancient Persians built qanats — underground water channels — to tap aquifers as early as 1000 BCE. Roman aqueducts sometimes drew from aquifer-fed springs. But the systematic understanding of groundwater as a geological phenomenon dates to the nineteenth century, when Henry Darcy published his 1856 study of water flow through sand in Dijon, France. Darcy's Law describes how water moves through porous media. The aquifer went from folk knowledge to physics.

The Ogallala Aquifer beneath the American Great Plains holds an estimated 978 trillion gallons of water — it is one of the largest underground freshwater reserves in the world. It irrigates 30% of U.S. cropland. But it is being depleted faster than it recharges. Some sections have dropped by more than 150 feet since the 1950s. The Latin word for water-bearer now names a resource that may not be there in a century.

Aquifer depletion is a global crisis. The Middle East, India, and northern China are all drawing down aquifers faster than rain refills them. Mexico City, built on a former lake, is sinking as its aquifer compresses. Jakarta is sinking too. The modern Latin word for water-bearer names the hidden resource that modern civilization assumed was infinite and is discovering is not.