There’s one source that provides almost a third of the water for all US agriculture. It’s called the Ogallala aquifer, stretching under the Great Plains from South Dakota to northern Texas.

Once considered inexhaustible, we now understand its limits.

For the first settlers in the Great Plains, water was scarce and farming was difficult…

Until the 1850s, when they began to use windmills to pump up groundwater from the aquifer. Suddenly they had all they needed and an agricultural boom was on.

Farmers and growing towns pumped water with abandon for a century, thinking it was being naturally recharged.

And it is, but so slowly that even that early pumping had begun to deplete it.

The Ogallala, it turns out, is what’s called fossil water. It was filled by the melt of continental ice sheets during Pleistocene ice ages. Some hydrologists think that took six million years.

But in the shallowest and thinnest parts of the aquifer, like in Texas and Kansas, its level has already fallen 100 to 200 feet. In a few places, it’s been completely drained.

This has spurred many states to regulate the use of the aquifer and many farmers to adopt more efficient irrigation systems and water conservation farming techniques.

We’ll need more of all three because we rely on the Ogallala for much of our water and food— and, hopefully, will be able to do so in the future.