You’ve probably seen the footage. It was 2015, and then-Mayor Eric Garcetti stood by the Los Angeles Reservoir as millions of small, black plastic orbs tumbled down the embankment like a slow-motion avalanche. It looked like a giant ball pit. It looked like a prank. Honestly, it looked like a bit of a disaster waiting to happen. But those 96 million shade balls in the LA reservoir weren't there for aesthetics. They were there to solve a very specific, very dangerous chemical puzzle that most people didn't even know was happening in their tap water.
Water is weird. When you store it in massive open-air basins like the 175-acre Ivanhoe or the Los Angeles Reservoir, nature starts messing with it immediately. You have birds. You have dust. But mostly, you have the sun.
The Bromate Problem Nobody Saw Coming
The real reason for the shade balls LA reservoir project wasn't actually about evaporation, though that’s what every headline claimed at the time. It was about bromate.
Here is the science, basically: Los Angeles gets a lot of its water from the California Aqueduct. That water naturally contains bromide. On its own, bromide is harmless. You could drink it all day. However, the LADWP (Los Angeles Department of Water and Power) treats that water with chlorine to keep it safe from pathogens. When bromide and chlorine meet up in a giant open-air tank and get hammered by UV rays from the California sun, they undergo a chemical reaction. They turn into bromate.
Bromate is a suspected human carcinogen.
The EPA sets strict limits on how much bromate can be in your drinking water. By 2008, the LADWP realized they had a massive problem at the Ivanhoe Reservoir. The sun was turning their clean water into a chemical liability. They needed a way to "turn off the lights" on 175 acres of water. You can't exactly put a roof on something that big without spending billions of dollars and taking a decade to build it.
Why Black? (And Other Design Quirks)
People always ask why they weren't white or chrome. Wouldn't white reflect the heat better?
You’d think so. But the goal wasn't just cooling; it was total UV blockage. The balls are made of high-density polyethylene (HDPE), which is the same stuff milk jugs are made of. To make them last 10 to 25 years in the scorching San Fernando Valley sun, they added carbon black. It’s a UV stabilizer. It prevents the plastic from getting brittle and breaking down into microplastics—well, that was the plan, anyway. If the balls were white, the UV rays would eventually penetrate the plastic, reach the water, and start the bromate reaction anyway. Plus, the plastic would have disintegrated in a few years.
They are four inches in diameter. They're weighted with about 210 milliliters of water so they don't just blow away when a Santa Ana wind hits.
Think about the scale for a second. Ninety-six million balls. Each one cost about 36 cents. That’s roughly $34.5 million spent on what looks like a childhood play place. Critics at the time called it a "gimmick." Some even argued that the balls would leach more chemicals into the water than they were preventing. But the LADWP was desperate. They had a federal mandate to cover the water, and this was the cheapest, fastest way to do it.
The Great Evaporation Myth
During the peak of the California drought, the narrative shifted. Everyone started talking about how the shade balls LA reservoir were saving 300 million gallons of water from evaporating every year.
That sounds huge. It’s not.
In the context of Los Angeles’ total water usage, 300 million gallons is a drop in the bucket. It’s enough for maybe 8,000 people for a year. For a city of four million? It’s rounding error stuff. Dr. Erfan Haghighi and his team later published a study in Nature Communications that pointed out something most people missed: it actually takes more water to make the plastic balls than they save through evaporation.
It takes about 700 million gallons of water to manufacture the 96 million HDPE balls.
So, if you’re looking at it strictly through the lens of "saving water during a drought," the shade balls were a net loss for the first couple of years. You have to keep them on the reservoir for nearly a decade just to break even on the "water footprint" of their production. This is the kind of nuance that gets lost in a 30-second news clip of a mayor throwing a ball into a lake.
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Maintenance and the "Inevitable" Microplastic Fear
What happens when you leave millions of plastic spheres floating in the sun for a decade?
Maintenance isn't exactly easy. You can’t just row a boat out there and start scrubbing them. The LADWP monitors the water quality daily. One of the biggest concerns among environmentalists is the degradation of the HDPE. While the carbon black helps, nothing is permanent. Over time, the friction of the balls rubbing against each other as the wind moves them creates physical wear.
Is there microplastic in the LA reservoir?
Technically, there’s microplastic everywhere now. But the levels found in the reservoir haven't triggered any health alarms yet. The LADWP argues that the alternative—building a massive, fixed-structure cover—would have involved significantly more carbon-intensive construction. They also point out that the balls are fully recyclable. When they reach the end of their life cycle, the plan is to haul them out, melt them down, and turn them into something else.
The Move Toward Floating Solar
If you visit the reservoir sites today, you’ll notice that the conversation is shifting. The shade balls LA reservoir project was a "V1" solution. It was cheap, it was fast, and it worked for the bromate issue. But the world has moved on to "floatovoltaics"—floating solar panels.
Why just block the sun when you can harvest it?
Floating solar does everything shade balls do: it blocks UV rays, reduces evaporation, and keeps the water cool (which also helps prevent algae blooms). But it also generates megawatts of clean energy. The cool water underneath the panels actually makes the solar cells more efficient than they would be on a hot roof.
LA hasn't fully swapped the balls for panels yet because of the sheer cost and the engineering challenge of anchoring panels on a reservoir that fluctuates in depth. But the shade balls paved the way. They proved that floating covers are a viable, large-scale solution for urban water management.
Lessons from the Ball Pit
What did we actually learn?
First, public perception is everything. The image of the shade balls went viral because it was tactile and easy to understand, even if the "evaporation saving" part was exaggerated. Second, engineering is often about the "least bad" option. The LADWP knew the water footprint of manufacturing was high. They knew plastic wasn't a "natural" solution. But they also knew they couldn't serve bromate to millions of people.
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How to Evaluate Water Solutions in Your Own Area
If you're following water infrastructure projects in your city, don't just look at the "green" headlines. Ask these questions:
- What is the primary goal? Is it chemical (like bromate), biological (algae), or physical (evaporation)?
- What is the total lifecycle cost? Not just the price tag, but the environmental cost to manufacture the solution.
- Is it temporary or permanent? Shade balls are a 20-year fix. A concrete cover is a 100-year fix.
- What is the byproduct? In this case, it’s the potential for microplastics and the heat absorption of the black surface.
The shade balls in the LA reservoir remain a fascinating case study in "emergency engineering." They weren't perfect. They weren't a miracle cure for the drought. But they kept the water legal and drinkable during a period of intense environmental stress.
As LA looks toward 2030, the balls will likely start to disappear, replaced by more advanced filtration systems or floating solar arrays. But for now, they sit there—96 million black dots bobbing in the sun, doing the boring, invisible work of chemistry.
Practical Steps for Interested Observers
For those interested in the future of urban water, keep an eye on the LADWP’s "Operation Next" initiative. This is the city's massive plan to recycle 100% of its wastewater by 2035. This will eventually make open-air reservoirs like the one in Sylmar less central to the daily distribution of drinking water, as the city moves toward advanced subsurface storage and indirect potable reuse.
Check your local water quality report. Every municipal water provider is required by law to provide a Consumer Confidence Report (CCR) annually. You can see exactly what your bromate and disinfectant byproduct levels are. If you live in an area with high sun exposure and open reservoirs, the "shade ball method" or its successors are likely the only reason those numbers stay within safe limits.
Don't be fooled by the simplicity of the solution. Sometimes, the most effective way to solve a complex chemical problem is just a whole lot of plastic and some basic physics.