Space & Innovation

What Ever Happened To Shade Balls?

Sunlight can cause a lot of damage to open-air reservoirs, which is why scientists created shade balls. What are they and how do they work?

If you've been to the Los Angeles area recently, you may have noticed that several of the city's famous open-air reservoirs have turned black. It's all good, though - the reservoirs are actually being covered by shade balls, an innovative solution to a long-standing problem. Jules Suzdaltsev explains in today's DNews dispatch.

Last year, L.A. city officials made a splash (heh) when they dropped around 96 million four-inch diameter plastic balls into the ginormous Los Angeles Reservoir. The Los Angeles Department of Water and Power (LADWP) had previously used the balls in smaller reservoirs, but this was a major deployment of a new and clever technology.

Shade balls are designed to do just that - float atop a water surface and shade the water beneath from sunlight. The balls were intended, in part, to reduce evaporation from the reservoirs, which were laboring under California's infamous drought. But more importantly, the technique put the city in compliance with a federal law requiring that drinking water reservoirs be covered.

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There are many good reasons to cover water reservoirs. There's the evaporation issue, of course. And after 9/11, many people worried that terrorist attacks could target municipal water supplies. But the most important reasons have to do with how water and sunlight interact.

When the EPA first enacted the mandate in 2006, it was responding to an outbreak of cryptosporidiosis, a stomach illness contracted from drinking contaminated water - often from open-air reservoirs. L.A.'s water supply was also vulnerable to a particular chemical reaction that happens when direct sunlight interacts with chlorine and bromide in the water. The reaction produces a chemical called bromate, which can be poisonous in high doses. The California reservoirs were also generating certain algae that combined with chlorine in dangerous ways.

The shade ball solution was one of several considered by city planners. It was chosen primarily because manufacturing the plastic balls was cheaper than other solutions, like giant roofs or tarps. The plastic is coated with a black carbon colorant that repels ultraviolet light and keeps the plastic from degrading.

Alas, some of the L.A. shade balls are being phased out. Floating covers are replacing the shade balls at two smaller city reservoirs. But the 175-acre Los Angeles Reservoir will continue to use the city's unique in-house solution.

-- Glenn McDonald

Read More:

NPR: LA Rolls Out Water-Saving 'Shade-Balls'

LA Times: A reservoir goes undercover

Gizmodo: Why Are Shade Balls Black Instead of White?