The U.S. population has grown by more than 50 percent since 1970, adding about 2.6 million people per year for four decades. The economy has also mushroomed during the same period, with the country's gross domestic product in 2018 rising from less than $1 trillion in 1970 to about $18.57 trillion in 2016.

Yet somehow, Americans now use less water per day than at any point since the 1960s.

That's according to a new report from the U.S. Geological Survey (USGS), which finds that U.S. water usage in 2015 was at the lowest level since before 1970, the most recent year for which data is available. Americans used about 322 billion gallons of water daily in 2015, down 9 percent from 2010.

"Reaching this 45-year low shows the positive trends in conservation that stem from improvements in water-use technologies and management," said Mike Connor, deputy secretary of the U.S. Interior Department, in 2014. "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."

Power plants, farms and public-supply withdrawals accounted for the majority of the country's water usage in 2015, at 90 percent, respectively. Thermoelectric power has grown more efficient in recent years, especially power plants, whose water withdrawals decreased by 18 percent since 2010, according to the USGS.

Morro Bay

California's Morro Bay Power Plant, built in the 1950s, was officially retired in 2014. (Photo: Shutterstock)

All thermoelectric power plants use water to make steam for electricity generation, but most withdraw even more water for cooling purposes. This water is often taken from local rivers, lakes, aquifers or oceans, and even though some is later returned (distinguishing "withdrawals" from "consumption"), both the withdrawal and the return of heated water can cause ecological problems. That's why many new power plants either reuse their cooling water or rely on advanced dry cooling techniques.

In 2010, crop irrigation was 9 percent leaner compared to 1970, explained USGS hydrologist Molly Maupin, largely due to the growing popularity of drip irrigation and other efficient watering methods. "Shifts toward more sprinkler and micro-irrigation systems nationally, and declining withdrawals in the West, have contributed to a drop in the national average application rate," Maupin said. However in 2015, irrigation withdrawals increased by 2 percent compared to 2010 but were still comparable to levels used in the 1960s.

Public water use in 2015 didn't fall quite as steeply, but was down 7 percent from 2010. I happened even though the U.S. population grew by 4 percent during the same period from 312 million people in 2010 to 325 million in 2015. Low-flow showerheads, toilets and other appliances are increasingly common in the U.S., as is the recycling of wastewater by cities and businesses.

U.S. water use

While this is good news, it offers little relief from historic droughts in California and other Western states. Some areas of the U.S. West are now drier than they've been since 1580, according to University of California-Berkeley paleoclimatologist B. Lynn Ingram, and this may just be a hint of drier days to come. A 2014 study suggests climate change is raising the odds of a megadrought in California, with up to a 50 percent chance of a three-decade dry spell this century. Meanwhile, agriculture is helping deplete groundwater supplies that can take centuries or even millennia to refill with rainfall.

California still leads the U.S. in water use, though, accounting for 9 percent of total withdrawals nationwide. Most of the water used was for irrigation. Texas, another arid state, is No. 2 with about 7 percent of all U.S. water withdrawals, and was primarily used for thermoelectric power and irrigation. It would be nice if voluntary efficiency efforts were enough, but some scientists and economists say the only true solution is to make the price of water reflect its availability. "Markets cannot work effectively," warns a 2014 policy paper by the Brookings Institution, "if users can delay facing the realities of local water scarcity through the unsustainable use of an open-access resource."

As of 2010, the U.S. also still withdraws more than 1,000 gallons of water per person every day, among the highest rates of per-capita water use worldwide. A 13 percent reduction over five years may seem like a drop in the bucket, but at least it's a drop in the right direction. Plus, it demonstrates an important point: The U.S. economy and population can continue growing even if our water use doesn't.

Editor's note: This article has been updated since it was originally published in November 2014.

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Americans use less water than they did in 1970
U.S. water usage is at a 45-year low, according to a new government report. But is that low enough?