Using ‘Shade Balls’ in Reservoirs May Use up More Water Than They Save

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Using ‘Shade Balls’ in Reservoirs May Use up More Water Than They Save

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

by Hayley Dunning

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Image credit: Eric Garcetti, Source: Imperial College London

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 drought, which lasted from 2011-2017, 96 million ‘shade balls’ were deployed on the Los Angeles reservoir. These floating, black plastic balls cover the water surface 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.

Solving one problem and creating another

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 up to an estimated 2.9 million cubic metres of water. During their time on the reservoir, the balls are estimated to have saved 1.7 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.

Environmental cost must be considered

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 negative effects 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, water 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.”

‘The water footprint of water conservation using shade balls in California’ by Erfan Haghighi, Kaveh Madani and Arjen Hoekstra  is published in  Nature Sustainability .

Source: Imperial College London

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8 Comments

  2. I do not agree, I think net water consumption comparing ball production and reservoir application is meaningless. At a minimum, the working life of the balls is very long, and their production could well be in an area where water availability is not an issue. Keep in mind that river water that is not utilized before treatment and discharge just ends up in the ocean without benefit. Increased evaporation when a reservoir is covered with balls does not seem to make thermodynamic sense.  Using white balls would certainly alleviate that if it were true, which I doubt.

  3. Congrats to the man from LONDON.  He hit the nail on the head..... with a jack hammer!  Man seems to be the most qualified at making mistakes and then quickly making them worst as soon as possible.  Try observational science. How does nature conserve water (and naturally clean it) ?  Apologies for using grade school examples, but must leave no doubt.  Test this yourself:  Take 3 equal bucket of water, one gallon each.  #1 pour onto a hot slab of concrete and allow to evaporate. measure the time. #2  set the next bucket in the same place but do not empty it. Measure how long it takes to evaporate.  #3 pour into a clear 10 foot tall plastic pipe 2 inches in diameter. Measure how long it takes to evaporate.

    As you can see our reservoir construction actually increases the evaporate rate.  By using natural formation with large overhangs it will decrease evaporation.  For any connective canals stop building the big U shaped and build a trapezoidal one instead. eg 3 feet on bottom and a one foot opening at the top.  This is the least expensive way to reduce loss and should allow sufficient time to decentralize water collection starting at residential and all buildings. Within 5 years the onsite biodigesters and biogenerators currently being used will become part of every construction project. $trillions of infrastructure costs and related health issues will be eliminated.

  4. I suppose it's worth asking if the water consumption to manufacture the balls is sustainable? I.e., if the plant can produce the balls and the associated water demand on their end can be sustained without adversely affecting supplies (I'm making an assumption that manufacturers are in a different geographical location than drought/implementation sites), the overall project may not be all that efficient or zero sum to do the 1.2 MCF difference, but it very well could be sustainable. 

  5. White "wiffle balls" would perform better as they don't retain the heat, they are white to reflect sun, not black absorbing heat, and the slots allow air exchange at night to cool water. And more importantly they are commercially available at a reasonable cost.

  7. has anyone looked at what happens to those plastic balls degrading in the sun and is there a micro plastic issue in the water as a result?

    1 Comment reply

    1. Microplastic particles is a question that has evolved in the press far beyond the data, which are undecipherable. There are about 50 published 'studies' that are fraught with analytical uncertainties and methodological flaws. The counts in drinking water are small -maybe up to about 100 per liter in some cases, including bottled water. The real exposures would be from filter feeders like mussels and oysters.  The potential risks are from particulates and potential transport of absorbed organic chemicals. The latter is possible but the quantities would be very small if they were desorbed after ingestion. (powdered carbon is an antidote for some poisonings). Some toxicants might actually be absorbed by particulates after ingestion. So, chemical transport to GI  is of questionable concern. Regarding particulate toxicity, keep in  mind that asbestos particles of a particular type and size aspect ratio are the concern. For perspective, the US drinking water standard is 10,000,000 fibers per liter longer than 10 microns. That exposure  never occurs.