Most Precipitation Evaporates
by Mateusz Perkowski
Thermoelectric power generation, which represents about 45 percent of
all U.S. water usage, is responsible for a large chunk of that water savings.
More than 4 trillion gallons of precipitation falls on the country every day on average. That's nearly enough to fill the Great Salt Lake in Utah.
But roughly two-thirds of that water almost immediately evaporates into the atmosphere or is used by plants.
Of the remaining water, which flows to the ocean in rivers or collects in lakes and underground aquifers, less than half can realistically be put to "intensive beneficial uses," according to a federal government report.
Since only a fraction of the nation's rainfall and snow is available to use, water managers have been understandably nervous about meeting the multitude of needs in the future -- particularly in the face of a larger population and warmer climate.
More people, less water
The good news is those worries have forced Americans to find ways to consume less water.
"It has helped us buck the conventional wisdom," said Heather Cooley, water program director for the Pacific Institute, a think tank that focuses on water issues.
Between 1950 and 1980, total withdrawals of surface and groundwater were outpacing the nation's population growth, according to the U.S. Geological Survey.
Water usage more than doubled in that time, from about 180 billion to 430 billion gallons per day, while the number of U.S. residents increased by about 50 percent.
The trend was clearly not sustainable, but water conservation efforts successfully changed that trajectory even as the population continued to increase.
"Ever since 1980, we've really seen a decoupling" of population growth and water use, Cooley said.
Water usage has leveled off or dropped in intervening USGS surveys, falling 17 percent to 355 billion gallons per day by 2010, according to the agency's most recent report. Meanwhile, the number of people in the U.S. has increased by more than 35 percent.
"It's a trend we see in communities across the U.S. and it's driven largely by efficiency improvements," said Cooley. "We saw declines in every single sector in 2010."
Thermoelectric power generation, which represents about 45 percent of all U.S. water usage, is responsible for a large chunk of that water savings.
Coal, nuclear and biomass plants rely on water for cooling and to produce steam to turn the turbine blades in their power plants. By recirculating water and making other upgrades, the facilities cut their water usage by more than 23 percent in three decades.
Irrigation, the nation's second-largest water user, has also reduced its consumption by 23 percent in that time, from 150 billion to 115 billion gallons per day.
Gravity systems, such as flood or furrow irrigation, were once the predominant forms of applying water in U.S. agriculture. They were overtaken in the 1990s by more efficient sprinklers, according to USDA.
Nearly 35 million acres of farmland were irrigated with sprinklers compared to 21.5 million acres irrigated with gravity systems in 2013, according to the USDA's latest data.
Irrigators who use sprinklers have also been switching to low-pressure systems that generate larger droplets than older, high-pressure systems, further conserving water, said Glenn Schaible, a USDA economist who studies water resources.
"You get a very high evaporation rate with high-pressure systems," Schaible said, adding that as droplets get smaller, they're more vulnerable to turning into vapor.
Drip, trickle and similar micro-irrigation systems, the most water-preserving available, were used on roughly 5 million acres in 2013.
Because the high-efficiency systems are also more expensive, farmers must justify them with greater revenues, Schaible said. "It occurs more in high-value crops than elsewhere."
Farmers benefit economically from conservation technology because they can stretch their available water to irrigate more acres, said Molly Maupin, a hydrologist for USGS.
Modernizing the conveyance of water has also helped reduce water usage in agriculture, she said. Lining canals with an impermeable layer impedes seepage, while replacing canals with pipes also prevents evaporation.
"The losses in transit are being minimized as much as possible," Maupin said.
Aside from getting more efficient at how water is applied, farmers make sure it gets to their crops at the right time.
Many farmers still apply water because "Dad irrigated that way" or based on the calendar date, but fewer than 10 percent of irrigators use more advanced tools such as soil moisture sensors and crop growth models, Schaible said.
"There's still a lot of room for improvement," he said. "That's where it takes management skill and knowledge."
With irrigation scheduling, farmers fine-tune their applications of water based on its availability in the soil and the crop's level of stress. The system aims to optimize irrigation without denting yields or using excessive water.
"It allows for more precision," said Cooley, noting that competing uses and scarcity drive growers to adopt new technology. "A lot of it comes down to the cost of water."
In some areas such as Oregon's Willamette Valley, there's a potential for irrigating acreage that's currently under dryland farming.
Only about 20 percent of the region is currently irrigated even though it has great soils, said Margaret Matter, water resource specialist for the Oregon Department of Agriculture.
Producers of nursery stock, stung by the impacts of the recent housing downturn, are diversifying into other crops that require irrigation, she said.
Hazelnut growers who are expanding their operations or replacing old orchards are also often choosing to install irrigation systems to boost yields, Matter said.
"There's certainly evidence that irrigation demand is increasing and will increase in the future," she said.
While it may be possible to make more water available from multipurpose flood control dams, farmers will still be constrained by their ability to recoup the added expenses.
"It may be so far away from any water source that it may be cost-prohibitive to build the conveyance system," Matter said.
Other water uses
Water usage in agriculture isn't limited to irrigating crops.
Livestock consume 2 billion gallons per day, a level that has largely remained stable since 1980.
Increased sales of farmed fish, on the other hand, has been correlated with significantly more water used in aquaculture.
Fish farms' sales topped $1.37 billion in 2013, which is about 40 percent more than 15 years earlier, according to the USDA's most recent Census of Aquaculture.
Aquaculture used 9.4 billion gallons a day in 2010, more than quadruple the amount used in 1985, when USGS began tracking it as an individual sector.
Residential and commercial users who depend on public supplies decreased their consumption by 5 percent from 2005 to 2010, to 42 billion gallons a day, but previously increased their usage by more than one-third since 1980.
Domestic homes with their own wells, which consumed 3.6 billion gallons per day in 2010, only used slightly more water than 30 years earlier.
Even with a swelling population, there's an opportunity to curtail domestic and commercial water use with more efficient appliances that also conserve money, said the Pacific Institute's Cooley.
"If you look at those savings, it's actually more than enough to cover the higher upfront cost," she said.
Cities were historically paved over to quickly steer precipitation into stormwater drains, minimizing the risk of flooding, Cooley said.
Now, more buildings are diverting water from gutters into cisterns or allowing it to seep into "bioswales" to recharge groundwater, she said. "Communities are starting to realize this is a source of supply."
Urban water users are thus beginning to emulate the industrial users, which recycle water.
Industrial users consume 16 billion gallons a day, down from about 45 billion gallons a day in 1980.
Many companies found an advantage in re-circulating water repeatedly, said Maupin. Because they discharge less, the cost of removing pollutants to comply with the Clean Water Act is reduced.
"It benefits them to re-use that water more and more inside their facility," she said.
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