Concrete Progress: LA’s Creative Approach to Freshwater Storage? Thousands of Plastic Balls

Concrete Progress is an ongoing series of columns by Peter Brewitt devoted to exploring America’s infrastructure. It is part of Orion’s Reimagining Infrastructure project.


The Los Angeles Reservoir, 175 acres of freshwater destined for the taps of our second-largest city, looks, to me, like an oil slick that has begun to freeze into some ghastly ice sheet. A closer look, though, reveals thousands of little plastic balls, bobbing about at the water line. They’re neither litter nor art installation, though Los Angeles is rich in both; they are, in fact, the most imaginative technique I’ve heard of for maintaining water quality and quantity in Southern California.

As you surely know, California has been enduring a horrifying, though not surprising, drought for the last several years—and while help may be on the way this winter, the situation remains pretty dire. There have been a lot of creative responses to the drought over the last few years, some of which I’ve written about here, here, and here, and which I assumed would be my last entryways to the topic for a while. But when, in mid-August, my Facebook feed drowned under a deluge of something called “shade balls,” I knew I had to revisit the Golden State and its water problems.

The people with the thankless task of watering four million Angelenos are employed by the LA Department of Water and Power. Urban water is a massive and intensely difficult issue—I often tell my students that if they get into urban water they will have jobs, and headaches, for life. Reservoirs in any city, but especially an arid one like Los Angeles, are subject to all manner of urban problems, from litter to the urban heat island effect. In 2005, the EPA released a rule upgrading the management of finished water reservoirs—reservoirs containing water that goes straight to the people without further treatment. New ones needed to come with a cover. Pre-existing reservoirs could either be covered or send their water to be treated, which is expensive. Some places have dealt with this by storing the water underground and building parks on top, but that idea, while good enough to mention here, is not feasible everywhere. How to cover an artificial lake?

The first thing you might think of would be a gigantic tarp, and it is, in fact, a popular idea. But to cover the LA Reservoir with some sort of floating tarp would cost hundreds of millions of dollars. A guy named Brian White, who worked for LADWP as a biologist, gets credit as the first to think of covering the water with floating objects, like an oversubscribed kiddie pool at a six-year-old’s birthday. He’d seen ponds at airports with balls to keep birds off the water (and out of 747 engines) and transferred the idea to LADWP’s reservoirs. As of mid-August, under the supervision of Mayor Eric Garcetti, the final 20,000 of 96 million balls rolled down the concrete and into the water. The total cost of the program is $34.5 million (36 cents a ball)—a pretty good deal compared to a new water treatment plant or a floating tarp system.

The balls have two functions. The most obvious one, of course, is shade. The balls will cover the water and prevent it from evaporating, saving an estimated 300 million gallons of water per year (LA consumes over a billion gallons a week, for a little perspective). Evaporation is one of the catch-22s of our Western water infrastructure—to have a desert civilization you must store water, but if you do, the same desert conditions that make water storage necessary will suck that water right up into the air. For instance, Lake Mead, the immense reservoir held back by the Hoover Dam, loses 800,000 acre-feet of water, or 2.6 trillion gallons, to evaporation every year. Shade balls present a nice, cheapish way to alleviate the problem.

The balls’ more important function, though, is to maintain water quality. As water gets warmer, algae blooms, and chemical reactions create pollution where there was none before. The central concern is bromate, which may cause cancer. Bromate is created when ozone, which is used for water purification, combines with bromide, which occurs naturally in water. UV light kickstarts the reaction (photoactivation is the term), and the result is a plague for water managers everywhere. Eight years ago, LADWP had to drain two of its reservoirs because of bromate pollution. The shade balls’ pigment, a substance called carbon black, maximizes their ability to absorb UV light, keeping it, and bromate, out of LA’s water.

I have to be honest. At first glance I figured that this was a really stupid idea and was expecting to say so here. And of course, it’s not ideal to produce millions of plastic balls—it would be better, say, to use less water. But other than this broad objection, there seem to be very few downsides to the approach. The balls, which I was sure would quickly bounce away and become trash, contain a little potable water themselves as ballast and cannot really go anywhere. Carbon black prevents them from breaking down under UV light, allowing them to last for decades. It’s a food-safe pigment, and is used as a food coloring in Australia and New Zealand. The balls are even made by a local company, called XavierC, which was founded in part to hire disabled veterans. The only downside, for some, is that Angelenos who are too creepy, sketchy, or shady in their pursuit of romantic attachments, are now known, in local parlance, as “shade balls.”

Peter Brewitt has wondered about infrastructure ever since a flood kept him away from three days of kindergarten. A professor of environmental studies at Wofford College, he is devoted to understanding how people decide to restore and remake their environments.


  1. Can someone please explain why they chose a dark plastic for the balls?
    Wouldn’t this accelerate warming and trap heat?
    e.g. it’s best practice to paint rooftops/other surfaces white to mitigate urban heat island effect.
    I’m hoping there’s some counterintuitive nuance.

  2. A plastic bottle takes two bottles of water to manufacture as it holds, those balls would take a similar amount. Since they were manufactured near the resivour one can assume they required a vast amount of that resivours water to manufacture them.

  3. Hi Ian. The use of carbon black maximizes the balls’ ability to absorb UV light, keeping it, and bromate, out of LA’s water. White balls would not have done as good a job.

  4. Hi Frank. The embedded water in our consumer goods is a great thing to bring up, something many people don’t think about. Since this is a finished water reservoir, intended to go straight to human consumption, I imagine that XavierC got the water somewhere else.

    The overall question, though, is how to cover a 175-acre reservoir. I would imagine that a tarp or some sort of tunneling system would be pretty resource-intensive also. Ideally, California would use less water, period, but in the meantime they have limited options to maintain the water they do use.

  5. A few relevant points:
    1. Open finished water reservoirs are polluted by birds and bird feces, mammal feces, dead animals, giardia, and more. To say the water is delivered to the public without further treatment is either a warning or (in many cases) a misleading statement since additional disinfection is applied.

    2. The water shortage in CA created a great hue and cry about Nestle bottling a very small amount–the real point as some protesters admitted being the use of plastic bottles. Here we have government using vastly greater amounts of plastic to deliver far inferior water. No hue and cry? Why?

    3. Water conservation is far more effective than evaporation control and CA hasn’t had the political backbone to either limit water use significantly or apply realistic pricing mechanisms. New Mexico (at least Santa Fe) has a pricing mechanism: each user has a reasonable amount at affordable rates. (The poor don’t pay more.) Above that prices go up rapidly to provide disincentives, and those who consume large amounts have their identities published so that consumers can choose whom to patronize.

    4. 80% of CA water is used by agriculture. Making ag water more expensive might increase food prices (the poor pay more in this case), but rising water prices could also incentivize water saving technology. (Think Israel.)

  6. Has anyone thought of a floating field of solar panels or does this reservoir get too rough? It would seem to be a good idea, if you are going to add plastic to a natural ecology, to use the situation to glean more renewable energy.

  7. It takes 1.3 gal to make a regular sized plastic bottle for soda or water according to research documented in my new book Your Water Footprint: The Shocking Facts About How Much Water We Use To Make Everyday Products. It took at least 150 million gallons of water to make all those plastic balls. Likely a lot more. However if those balls last for ten years then was probably worth it.

  8. Wouldn’t there potentially be some toxicity to those plastic balls? …which would be leeched into the water. Just saying.

  9. Hi everyone. Wallace brings up some really good points about the embedded water in our consumer goods, and about the real water consumption culprit in California being ag. At the same time, the ubiquity of industrial water means that pretty much anything they might have used to cover the reservoir would have been pretty water-intensive.
    There are some water conservation/consumption disincentives rules in various California towns (my old home of Santa Cruz, for instance), but state-level action on that will probably not happen in the next 50 years, and in the meantime, LA had to cover its water.
    Jean, that’s a good idea, but I don’t think you’d be able to use floating solar panels in and of themselves – you’d have to cover it with something first. Using covered reservoirs to make solar seems a solid thought to me overall.
    Stephen, thanks for the info. The book sounds cool.

  10. Hi Michelle. Some plastics are indeed toxic, but (as far as I know) not this kind. The thing here is, there is no better way to cover the reservoir and maintain low bromate levels. The other options would either be far more expensive (digging an artificial aquifer, more or less) or also made of plastic (a huge tarp), or both. If you know of a better option, definitely please post about it. Most of the natural materials that I can imagine using would probably fall apart or rot pretty quickly.

    Just to be clear, I’m no fan of plastics. But it seems to me that LA has found the least-bad option, and pretty creative one at that.

  11. Let aside the aspects linked to plastic, pollution, waste of resources and money, I understand from the numbers you give in the article that the balls save about 2 days worth of water usage in a year. I am not sure if this is a great achievement.
    I feel like there could be cleverer and wiser ideas to catch that water amount (fixing leaks, improving water catchment and storage in the urban area, implement water saving strategies in the households).
    This seems an additional step in the wrong direction, a cure for symptoms not of root problems, causing more problems than it fixes.
    How much is the overall evaporation of the reservoir by the way (I don’t understand why the overall evaporation is given for a different site and not the one concerned by the article)?

  12. Hi FR. The thing to bear in mind here is this: LADWP was required to cover its reservoir by the EPA. They didn’t have the option of attacking water supply from the consumption end and calling it good.The central reason that they had to do this was to maintain water quality – the bromate issue – which requires them to fight UV light with some sort of barrier. The balls’ savings on evaporation are a benefit but are not their main point. LADWP does do a variety of things to reduce consumption (native landscaping programs and so on), but those would be a separate column.

    The only numbers I’ve seen on evaporation from the LA Reservoir are the 300 million gallons in savings – this is not the entire annual evaporation from the reservoir, but it shows the kind of quantities we’re dealing with. I included evaporation from Lake Mead as am example of the broader phenomenon of evaporation loss from Western reservoirs.

    It would be great to brainstorm some better solutions to cover a reservoir. Does anyone reading this have anything to suggest?

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