Back in 2015, a video caught people’s attention, asking an unusual question: why were there 96 million black plastic balls floating atop a reservoir in Los Angeles? Many initially guessed that they were there simply to reduce water loss during California’s severe drought by blocking sunlight and cutting down evaporation.
However, the real reason behind these mysterious balls was much more surprising and important. These black spheres, known as “shade balls,” were actually introduced to safeguard the quality of the city’s drinking water. Open reservoirs exposed to sunlight face a hidden problem: ultraviolet rays can react with substances naturally found in the water, particularly bromide. When chlorine is used to disinfect the water, this reaction can create a harmful chemical called bromate.
Bromate is linked to cancer, and the Environmental Protection Agency (EPA) has strict limits on its presence in drinking water. Officials in Los Angeles found that their reservoir, under intense sun, was at risk of producing this dangerous chemical. They needed a fast, cost-effective way to cover the water’s surface and block sunlight. This is where the shade balls came into play. Each ball is made of sturdy, food-safe plastic, filled with a bit of water to keep it steady, and coated with a carbon-black pigment that blocks UV rays. When millions of these balls spread across the reservoir, they form a floating shield that protects the water from sunlight.
This simple yet clever idea brought several benefits. It prevented the creation of bromate, kept dust and debris out of the water, discouraged birds from landing, and also helped reduce evaporation as a bonus. Initially, many people found the idea odd or wasteful. Critics questioned the cost of producing so many plastic balls and wondered if it was just a publicity stunt during the drought. But the project proved to be a smart and effective solution.
The total cost to produce and deploy the shade balls was about $34.5 million, but the benefits outweighed this expense in the long run. The reduced evaporation saved nearly 300 million gallons of water each year—enough for thousands of homes. More importantly, preventing chemical pollution meant avoiding costly water treatments and staying in compliance with EPA rules. Experts noted that while shade balls might not fit every water storage situation, they were perfect for Los Angeles at that moment.
Other options, like building large metal or fabric covers, would have been much more expensive and taken years to build. Shade balls, on the other hand, could be made and spread quickly within weeks. The special carbon-black coating was chosen to protect the plastic from breaking down under the sun, allowing the balls to last up to 25 years. When the city’s water department announced the project, they emphasized that the science was solid and that this innovative approach solved multiple problems simultaneously.
Over time, the floating black balls stopped being a strange oddity and became a symbol of smart and creative problem-solving. For Los Angeles residents, they represented how unusual ideas can lead to effective solutions. What began as an internet curiosity about why millions of black balls were dumped into a reservoir ended up showing the vital importance of protecting water safety amid environmental and health challenges. This project highlighted how engineering, science, and thinking outside the box can tackle tough problems in unexpected ways.
In the end, the shade balls were not just about saving water through reduced evaporation, although that was a real bonus. They were about safety, chemistry, and making sure millions of people could trust the water from their taps every day. By turning simple plastic spheres into a protective shield, Los Angeles found an ingenious way to preserve its water quality, while the world watched in wonder at the sea of black balls shimmering under the California sun.
