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 rising by 218 percent, from less than $5 trillion to about $15 trillion.

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 hit a 45-year low in 2010, the most recent year for which data are available. Americans used about 355 billion gallons of water daily in 2010, down 13 percent from 2005 and 4 percent from 1970.

"Reaching this 45-year low shows the positive trends in conservation that stem from improvements in water-use technologies and management," says Mike Connor, deputy secretary of the U.S. Interior Department. "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 and farms account for the majority of the country's water usage, at 45 percent and 33 percent, respectively. Both have grown more efficient in recent years, especially power plants, whose water withdrawals decreased by 20 percent from 2005 to 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.

Crop irrigation has also become 9 percent leaner since 1970, explains 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 says.

Public water use hasn't fallen quite as steeply, but it is down 5 percent from 2005. That marks the first decline in public withdrawals since at least 1950, and it happened even though the U.S. population grew by 4 percent during the same period. 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 recent 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 11 percent of total withdrawals nationwide. Texas, another arid state recently plagued by drought, is No. 2 with about 7 percent of all U.S. water withdrawals. 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 recent 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."

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.

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