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This means shade balls would need to stay on the Los Angeles Reservoir for at least a year or more to save water. Depending on exactly where the shade balls are made, it could take up to 2.5 years to recover the water used.

Haghighi said people need to consider environmental conservation on a global scale, rather than just a local one. They must also consider the entire life cycle of the technology. If the water saving the Los Angeles Reservoir comes at the cost of consuming water in other parts of world, Haghighi said, is it worth it?

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The water saved from evaporation by shade balls is small compared to other water-saving strategies, said Aditi Bhaskar, a hydrologist at Colorado State University, who wasn’t involved with Haghighi’s study.

At the time, Californians faced a record-setting drought, and conserving water was on everyone’s minds. Mandatory water restrictions led to brown lawns and shorter showers.

Haghighi’s team estimated that manufacturing 96 million shade balls required between 66 and 766 million gallons of water — the equivalent of 100 to 1,000 Olympic-sized swimming pools. This large range is due to the thickness of the balls, which can vary dramatically.

The team found a range of previously published estimates of water use for these three resources. Because manufacturing practices vary around the world, the researchers collected both local values for water consumption and a global average.

Since shade balls have stayed on the Los Angeles Reservoir since 2015, they are likely now starting to save more water than they cost to produce.

But a new study raises an interesting question: Could saving water in the Los Angeles Reservoir come at the cost of consuming water in other parts of world?

A 2014 study showed that of all the water saving strategies used in LA in 2010, mandatory restrictions of water use — essentially stopping people from watering their lawns — saved the most water.

The Los Angeles Department of Water and Power said the shade balls could keep contaminants out of the water and reduce the evaporation of the reservoir by 85 to 90 percent during a drought. The officials said the annual savings could amount to up to 300 million gallons of water, enough to supply drinking water to 8,100 people.

To estimate the amount of water it takes to make shade balls, the MIT team conducted what’s known as a “blue” water footprint — an analysis that estimates the amount of water used in the process of manufacturing a product. In this case, the shade balls are made of a plastic called polyethylene.

The shade balls could still be useful during a drought if a reservoir accounts for when and where these shade balls are made, said Jay Lund, director for the Center for Watershed Sciences at the University of California Davis. If the shade balls, or other water-sapping technologies, are made during periods when water is abundant, the net effect of manufacturing may be zero.

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Amanda Grennell is PBS NewsHour’s 2018 AAAS Mass Media Science & Engineering Fellow. She recently earned a doctorate in chemistry from the University of Colorado Boulder as a NSF Graduate Research Fellow. Outside of the lab, Grennell acted as senior editor for the graduate student blog Science Buffs, artistic director for the first annual ComSciCon Rocky Mountain West and a writer and social media manager for Chembites.

The team cautioned that water savings from the shade balls will likely be less than 300 million gallons during years when there is no drought. That’s because evaporation of water decreases when the air isn’t as dry. The actual period of time needed to recover water from shade ball manufacturing might even be longer.

The LA Department of Water and Power said they plan to keep shade balls as a permanent solution to water quality issues on the Los Angeles, replacing them every 10 years. LA officials also deployed shade balls at three other reservoirs, between 2008 and 2012, where they stayed temporarily for five to nine years.

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Haghighi’s team then examined industry reports from plastic manufacturers to determine how much oil, natural gas, and electricity goes into making polyethylene.

“We know that high-density polyethylene itself is made using oil, natural gas, and electricity,” said Erfan Haghighi, an environmental scientist and mechanical engineer at MIT, and lead author on the paper. “And each of these energy sources are water intensive.”

The creators of shade balls originally used them to prevent chemical treatments in the reservoir from reacting with sunlight and creating bromate, which is a carcinogen regulated by the EPA. California began deploying shade balls in 2008 as a cost-effective way to reduce bromate levels and also prevent algae growth. The LA Department of Water and Power picked shade balls over other, more expensive covers for the city’s biggest reservoir that would have cost an extra $250 million dollars.

“With water, the impacts are much more local, both in time and space,” Lund said “It’s quite plausible to manufacture shading materials at a time and a place where water is relatively abundant and employ them to reduce evaporation at a time in the place when water is really valuable.”

Shade balls cover the surface of the 175-acre Los Angeles Reservoir. By blocking sunlight, shade balls decrease levels of bromate, a carcinogen, which forms when sunlight reacts with treated water and naturally occurring bromine. Photo by Patrick T. Fallon/Bloomberg via Getty Images

Left: In 2015, 96 million plastic "shade balls" were tossed into the Los Angeles Reservoir to improve water quality and save some water. Image by Eric Garcetti/via YouTube

From there, they calculated how much plastic, oil, natural gas, electricity and water went into making the 96 million shade balls.

But a team from the Massachusetts Institute of Technology, Imperial College London and University of Twente in the Netherlands reported Monday that it may take more water to make the shade balls than what they save. To offset this loss, the shade balls must sit on the Los Angeles Reservoir between 1 to 2.5 years.

Shade balls have lowered bromate levels and stopped algae growth on several reservoirs in the Los Angeles area. They were first used in 2008 on the Ivanhoe Reservoir.

“Savings in just May through June 2010 [with mandatory water restrictions] is 10 times larger than the 300 million gallons which they’re getting per year for the shade balls,” Bhaskar said.

In 2015, the world watched as a video of 96 million “shade balls” getting dumped into the Los Angeles Reservoir went viral. The purpose of the balls: to improve water quality and save water.