DENVER (AP) — The intensifying crisis facing the Colorado River amounts to what is fundamentally a math problem.

The 40 million people who depend on the river to fill up a glass of water at the dinner table or wash their clothes or grow food across millions of acres use significantly more each year than actually flows through the banks of the Colorado.

In fact, first sliced up 100 years ago in a document known as the Colorado River Compact, the calculation of who gets what amount of that water may never have been balanced.

"The framers of the compact — and water leaders since then — have alway...