Using 'shade balls' in reservoirs may use up more water than they save

July 16, 2018, Imperial College London
The final deployment of shade balls at the LA Reservoir in 2015. Credit: Eric Garcetti

Preventing reservoir evaporation during droughts with floating balls may not help conserve water overall, due to the water needed to make the balls.

During droughts, communities may rely on water stored in reservoirs. However, significant amounts of water can evaporate from the surface of the reservoir.

Amid California's latest , which lasted from 2011-2017, 96 million 'shade balls' were deployed on the Los Angeles reservoir. These floating, black plastic balls cover the to prevent evaporation.

However, a new study published today in Nature Sustainability shows that producing the balls probably used more water elsewhere than was saved during their deployment—which could have knock-on environmental impacts.

The balls were deployed on the reservoir for one and half years during the latter part of the drought. For each drop of water saved by the balls, however, the study estimates that more than one drop would have been used up in another part of the country or the world.

Co-author Dr. Kaveh Madani, from the Centre for Environmental Policy at Imperial College London, said: "We are very good at quick technological fixes, but we often overlook the long-term and secondary impacts of our solutions. This is how the engineering community has been solving problems; solving one problem somewhere and creating a new problem elsewhere."

The shade balls are made of a kind of plastic that requires oil, natural gas and electricity to produce, all of which require large quantities of water. Producing 96 million balls of standard 5mm thickness would use an estimated 2.9 million cubic metres of water. During their time on the reservoir, the balls are estimated to have saved 1.15 million cubic metres of water.

The study team from Imperial, M.I.T. and the University of Twente predict the balls would have to be deployed for two and half years before the water they saved matched the water they used.

However, this is only if they were preventing evaporation at the same rate even outside the dry period; when not in drought conditions, the balls are expected to be less efficient at preventing evaporation, meaning they would have to be deployed for longer to save as much water as they used.

This is alongside other potentially on the water, such as affecting life in the reservoir or promoting bacterial growth. In addition, the balls' production could have negative effects on the environment associated with water pollution or carbon emissions.

As more extreme temperatures and more frequent droughts are predicted to occur due to climate change, management will become an important topic in the coming decades. Dr. Madani said: "We are not suggesting that shade balls are bad and must not be used. We are just highlighting the fact that the environmental cost of shade balls must be considered together with their benefits."

Explore further: Worms found in Scottish water supply

More information: Erfan Haghighi et al, The water footprint of water conservation using shade balls in California, Nature Sustainability (2018). DOI: 10.1038/s41893-018-0092-2

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not rated yet Jul 16, 2018
Imagine all the toxic crap leaching from the balls as they are photodegraded by UV light.
5 / 5 (1) Jul 16, 2018
Why black? Black is better at absorbing heat and increasing the temperature of the water, which increases evaporation. No?

I saw a photo of a reservoir somewhere covered by solar panels. Two birds with one stone!
5 / 5 (1) Jul 16, 2018
I thought about the coloring too. Because the plastic is thin (to reduce cost, enhance flotation, etc.), a non-colored plastic would have been almost transparent, which would have let sunlight through to the water, heating it up and allowing algae to grow. Because the hollow plastic ball floats so high, very little of its surface actually touches the water, so less heat is transferred from the ball to the water. Also the heating is occurring from above, leading to stratification of air in the ball, with hot above and cool below, further limiting heat transfer. And finally, the heating inhibits algal growth on the balls themselves.
1 / 5 (1) Jul 16, 2018
Another "brilliant" idea from the AGW Cult.
Yep, they'll save the world.
not rated yet Jul 16, 2018
"However, a new study published today in Nature Sustainability shows that producing the balls probably used more water elsewhere than was saved during their deployment"

I agree it's not the best idea to use 3 gallons of water to save 1, but at the same time, you're saving the water where it needs to be saved. This article is like telling a man dying of thirst in the desert, that there's plenty of water in the ocean just 100 miles away, rather than giving him some water. Emergencies create waste, and thats pretty much unavoidable.
Jul 17, 2018
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Jul 17, 2018
This comment has been removed by a moderator.
1 / 5 (1) Jul 17, 2018
Why black?

The color isn't important (shade balls elsewhere have any number of colors). The shade balls in question are black due to an additive that makes them UV resistant.

The idea of shading a water area could probably be solved in a better way (e.g. floating wooden structures)

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