Back in 2015, a video went viral asking a strange question: why were there ninety-six million black plastic balls floating on top of the Los Angeles Reservoir? At first glance, people assumed the reason must have been something simple like reducing evaporation during California’s historic drought.
After all, covering the surface of a massive open-air water storage facility with millions of spheres could block sunlight and slow down how fast water disappeared into the dry air. But the real reason behind this odd sight was much more surprising—and in many ways, far more important than just saving water. The black balls, officially called “shade balls,” were deployed as a safety measure to protect the quality of Los Angeles’ drinking water. Open-air reservoirs face a hidden problem when exposed to the sun: ultraviolet light reacts with certain naturally occurring substances in the water, especially bromide, and when chlorine is added as part of water treatment, the reaction can produce a dangerous chemical byproduct called bromate.
Bromate has been linked to cancer, and the Environmental Protection Agency (EPA) has strict limits on how much is allowed in public drinking water. Los Angeles officials realized that their reservoir, sitting under blazing California sun, was at risk of forming these harmful compounds. They needed a solution that could cover the massive surface of the water quickly and cost-effectively. Enter the shade balls. Each one is made from durable, food-grade plastic, filled with a little bit of water so it stays in place, and coated with a carbon-black pigment that blocks UV rays. When millions of these balls are released across a reservoir, they form a floating cover that prevents sunlight from penetrating the surface.
This simple idea ended up providing several benefits at once: it stopped bromate from forming, protected the water from dust and debris, discouraged birds from landing in the water, and yes, even reduced evaporation as a side effect. At first, many people mocked the idea, calling it strange or wasteful. Critics joked about the cost of making so many plastic spheres and questioned whether it was just a publicity stunt during California’s drought crisis. But in reality, the shade balls turned out to be a practical solution.
Producing and deploying them cost around $34.5 million, but the long-term savings were substantial. By reducing evaporation, the reservoir was estimated to save nearly 300 million gallons of water each year—enough to supply thousands of households. Even more importantly, keeping the water safe from chemical contamination meant the city avoided expensive treatments or the risk of violating EPA standards. Scientists and engineers pointed out that while the balls weren’t a perfect solution for every kind of water storage, they were uniquely well-suited for Los Angeles at the time.
The alternative options, like building giant metal or fabric covers, would have been far more expensive and taken years to construct. Shade balls, on the other hand, could be manufactured and spread over the water in a matter of weeks. The carbon-black pigment used in the balls was also chosen carefully to make them last. Without it, sunlight would have broken down the plastic quickly. With it, the shade balls were expected to float safely for up to 25 years. When the city’s Department of Water and Power officials unveiled the project, they explained that the science was sound and that this approach was an innovative way to solve multiple problems at once.
Over time, the sight of millions of black spheres shimmering across the reservoir became less of a curiosity and more of a symbol of creative problem-solving. For Los Angeles residents, it was a reminder that sometimes the strangest-looking solutions can turn out to be the smartest. What began as a viral internet mystery—why would anyone dump 96 million black balls into a lake—ultimately highlighted the importance of protecting water quality in the face of both environmental threats and public health concerns. The project showed how engineering, science, and a bit of out-of-the-box thinking could tackle complex problems in unexpected ways.
In the end, the shade balls weren’t just about evaporation, even though that benefit was real. They were about safety, chemistry, and making sure millions of people could trust the water that came out of their taps every single day. By turning something as simple as plastic balls into a barrier against harmful reactions, Los Angeles found an innovative way to keep its water safe and usable, while the rest of the world watched in amazement at a sea of black spheres bobbing under the California sun.
