The Green Bridge passes over full water levels at a section of Lake Oroville near the Bidwell Marina on July 20, 2011, in Oroville, California. (Paul Hames/California Department of Water Resources/Getty Images)

With all the images of the drought-plagued, dried-up waterways of California (see above), and a growing population and economy, it's easy to assume that the U.S. would actually use more water now, than say, 40 years ago.

But, according to a United States Geological Survey (USGS) report, the opposite is actually true: As of 2010, the U.S. now uses less water (355 billion gallons per day) than in 1970.

The latest statistics continue a marked trend of declining water use in the U.S. since 2005, the report states. In fact, water usage declined by 13 percent overall during the five year period from 2005 to 2010.

As Vox points out, there's a big difference between what this study measures, water withdrawal, and what might immediately come to mind, water consumption. Simply put, water withdrawal is a measure of all water taken from natural water sources, even water that is recycled back into the rivers, streams, etc., whereas water consumption only accounts for the water that's not recycled back into a natural source, like water used for irrigating crops.

(MORE: Watch 13 Years of Drought in 30 Seconds)

Still, that number is declining, even when, as Peter Gleick of the Pacific Institute notes, one might assume that a growing population and economy would increase demand for water across the country.

(Peter Gleick, Pacific Institute)

So what's the deal?

One part of the explanation is pretty simple: New technology is making it possible for the biggest water users to use less water. The biggest culprits have long been thermoelectric power sources, which use large quantities of water to power steam generators and cool equipment, and crop irrigators, which is a bit more self explanatory.

For example, back in 2005, thermoelectric power contributed to 50 percent of all water use in the U.S. And thermoelectric power was still the biggest user in 2010, too, but the total amount of water withdrawn by thermoelectric power plants dropped by 20 percent from 2005 to 2010. That's because many of the U.S.'s thermoelectric power plants were either built or converted to utilize "cleaner" technology like water recycling and dry cooling, the USGS notes.

The same goes for irrigation sources, too, which dropped water use by 9 percent thanks to more efficient watering systems.

“Reaching this 45-year low shows the positive trends in conservation that stem from improvements in water-use technologies and management," Mike Connor, deputy secretary of the Interior, said in a press release. “Even as the U.S. population continues to grow, people are learning to be more water conscious and do their part to help sustain the limited freshwater resources in the country.”

(USGS)

Of course, a reduction of water use as a whole matters less when there's less water to use as a whole. That's the case in California, where the state's worst drought in recorded history has sucked water sources completely dry.

And shockingly, despite its water woes, California was still the worst water using state by far in the report, accounting for 11 percent of all water use in 2010, (albeit before the drought began).

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