In 2015, millions of black plastic balls rolled across the surface of a reservoir in Los Angeles, creating an image that quickly travelled far beyond California.
asserted
that → roll → California
The 96 million shade balls were placed on the water during a severe drought, with a practical purpose: reducing evaporation while also helping protect drinking water from sunlight-related chemical reactions.
asserted
balls → place → reactions
At first glance, the idea appeared straightforward: cover the reservoir, block the sun and keep more water in the system.
asserted
idea → appear → system
But there was another part of the calculation that was harder to see.
asserted
that → be → calculation
The plastic balls themselves required water to manufacture.
asserted
balls → require → water
A 2018 study examined that hidden water use and found that the environmental equation was more complicated than the reservoir alone suggested.
uncertain
reservoir → examine → use
Why Los Angeles covered its reservoir with plastic balls
The shade balls were not introduced simply as a way of dealing with evaporation.
asserted
balls → cover → evaporation
Los Angeles had already been using them before the spectacular 2015 deployment, beginning in 2008.
asserted
Angeles → use → 2008
One of their purposes was to keep sunlight from triggering chemical reactions in treated reservoir water.
asserted
One → keep → water
Sunlight can contribute to the formation of bromate when it interacts with naturally occurring bromine in water that has been treated with ozone.
asserted
that → contribute → ozone
Bromate is regulated as a carcinogen by the US Environmental Protection Agency.
asserted
Bromate → regulate → Agency
According to PBS, blocking sunlight also helped limit algae growth.
uncertain
blocking → accord → growth
For Los Angeles officials, shade balls offered a relatively inexpensive way of dealing with these water-quality concerns.
asserted
balls → offer → concerns
Other types of reservoir covers had been considered, but the alternatives could have cost the city around $250 million more.
uncertain
alternatives → consider → more
The drought added another reason to expand their use.
asserted
drought → add → use
How 96 million shade balls helped Los Angeles save reservoir water
The Los Angeles Reservoir covers about 175 acres, and in 2015 the city completed the installation of roughly 96 million shade balls across its surface.
The Los Angeles Department of Water and Power estimated that the balls could reduce evaporation by around 85 to 90% during drought conditions.
uncertain
balls → help → conditions
At the upper end of its estimate, the annual saving could reach about 300 million gallons of water, enough to supply roughly 8,100 people.
uncertain
saving → reach → people
That figure, however, describes what happens at the reservoir.
asserted
what → describe → reservoir
It does not account for the water consumed before the balls ever reach Los Angeles.
asserted
balls → account → Angeles
This was the question examined by researchers from the Massachusetts Institute of Technology, Imperial College London and the University of Twente in the Netherlands, as reported by Nature Sustainability in a July 2018 research paper.
asserted
This → examine → paper
PC: National Geographic
Researchers calculated the water footprint of 96 million shade balls
The researchers looked at the water footprint of manufacturing the shade balls rather than treating them as if they appeared at the reservoir without an environmental cost.
asserted
they → calculate → cost
The balls are made from polyethylene, a plastic whose production depends on oil, natural gas and electricity.
asserted
production → make → oil
Producing each of those inputs can consume substantial amounts of water.
asserted
Producing → produce → water
The amount varies according to where and how the materials and energy are produced.
uncertain
materials → vary → ?
The team combined previously published estimates of water consumption with information about the quantities of oil, natural gas and electricity required to manufacture polyethylene.
asserted
team → combine → polyethylene
It then used those figures to estimate the water involved in producing the huge batch installed at the Los Angeles Reservoir.
asserted
It → use → Reservoir
Up to 766 million gallons of water may have been used
uncertain
gallons → use → water
The researchers estimated that producing the 96 million shade balls consumed somewhere between 66 million and 766 million gallons of water.
asserted
producing → estimate → water
The difference between the two figures was largely linked to uncertainty over the balls' thickness.
asserted
difference → link → thickness
Manufacturing conditions and the location of production also affected the calculation.
asserted
conditions → affect → calculation
To put the numbers into perspective, the researchers compared the amount with Olympic-sized swimming pools.
asserted
researchers → put → pools
Reportedly, the estimated manufacturing water footprint ranged from the equivalent of roughly 100 to 1,000 such pools.
uncertain
footprint → estimate → pools
That does not mean the balls permanently used up all of that water in the same place.
asserted
balls → mean → place
The point was that water had already been consumed somewhere in the production chain before the balls could begin saving water in Los Angeles.
uncertain
balls → consume → Angeles
The balls needed time to make up the difference
Based on their calculations, the researchers estimated that the shade balls would need to remain in place for between one and 2.5 years before the water saved through reduced evaporation could offset the water consumed during their production.
uncertain
water → need → production
The exact period depended on manufacturing conditions and the associated water use.
asserted
period → depend → conditions
By the time the study was published in 2018, the balls had already been covering the reservoir since 2015.
asserted
balls → publish → 2015
That meant they were likely moving beyond the initial period in which their manufacturing water footprint outweighed the water they had helped retain.
asserted
they → mean → water
During drought, when conditions are hotter and drier, preventing evaporation can save considerably more water.
asserted
preventing → prevent → water
In wetter or less dry periods, the amount of water naturally lost from the reservoir falls.
asserted
amount → lose → reservoir
…and 24 more, not listed.
The Aporia
