Question: Since the year 1900, how many liters of water have been sucked from the world's underground aquifers?
Answer: 4500 trillion. That's 4500 cubic kilometers. And we're currently draining away another 1000 cubic kilometers every year.
Why is this important? Because in many parts of the world, agriculture and other human uses rely crucially on underground water supplies.
And in much of the world, we're exhausting those supplies. This is becoming a crisis in many arid and semi-arid regions, where centuries of accumulated water are being quickly used up.
China, India, and the U.S. are the biggest over-consumers. The worst-affected areas include the western U.S., Mexico, the northwestern Sahara, the Indus Basin, and the North China Plain.
What are the implications? Among other things, higher food prices.
As the human populace continues to climb, that will have an impact on us all.
Water is a big concern today. It'll be an even bigger worry tomorrow.