The Colorado River Basin has lost as much groundwater as the entire volume of Lake Mead

Deep below the surface of the ground in one of the driest parts of the country, there is a looming problem: The water is running out — but not the kind that fills lakes, streams and reservoirs.

​ Deep below the surface of the ground in one of the driest parts of the country, there is a looming problem: The water is running out — but not the kind that fills lakes, streams and reservoirs. Read More Breaking News, Latest News and Videos | CNN