Millions of black plastic balls floating on drinking water supplies may seem like an environmental disaster, but for Los Angeles, they turned out to be a simple solution to several major challenges. This unusual sight attracted worldwide attention and left many wondering why a city would deliberately cover its water supply with 96 million plastic shells. Far from being a publicity stunt, floating “shade balls” were introduced by the Los Angeles Department of Water and Power (LADWP) to conserve water during California’s severe drought, protect drinking water quality, and meet strict environmental regulations. The project became one of the world’s most innovative and cost-effective examples of modern water management.
What are the black balls that spilled into Los Angeles’ drinking water?
The black balls are hollow plastic spheres known as shade balls, each about 10 centimeters (4 in) in diameter. Made from high-density polyethylene (HDPE), a durable plastic commonly used in water pipes and milk bottles, each ball contains a small amount of water to keep it stable and protected from being blown away by strong winds. The Los Angeles Department of Water and Power (LADWP) released all 96 million shad balls into the Los Angeles Reservoir in August 2015, the largest shad ball project in the world at the time. The carbon black coating protects the plastic from ultraviolet (UV) radiation, giving the balls an expected lifespan of about 10 years.The Los Angeles Reservoir covers approximately 175 acres (71 ha). Engineers calculated that approximately 96 million shadow balls were needed to cover most of the water surface. Instead of forming a rigid layer, the balls float freely and automatically adjust as the water level rises and falls. Together, they form a protective blanket that blocks out sunlight and allows the reservoir to function normally.
Reducing evaporation during California’s drought.
The primary objective of the project was to conserve water. Southern California often experiences prolonged drought, and large open reservoirs lose significant amounts of water through evaporation under intense sunlight. By shading the surface, the balls reduce the amount of solar energy reaching the water, helping to reduce evaporation. LADWP estimated that the project could save approximately 300 million gallons (about 1.1 billion liters) of water each year, enough to supply thousands of homes annually.
Preventing bromate formation
While saving water was important, protecting the quality of drinking water was an even bigger priority. The reservoir contains naturally occurring bromide, which may react during the water treatment process. After water is disinfected using ozone, bromide can be converted to bromate by exposure to sunlight, a chemical classified as a probable human carcinogen by the International Agency for Research on Cancer (IARC). Since California has strict limits on bromate levels in drinking water, blocking sunlight significantly reduces the chance of this reaction occurring.
Keeping algae, birds and debris under control
Shade balls provided several additional benefits. By reducing sunlight, they limited algae growth, which helped maintain water quality and reduce treatment requirements. They also discouraged birds from landing on the reservoir, reducing the risk of contamination from feces. Additionally, the floating layer reduced the amount of dust, leaves, and other wind-blown debris entering the water, making the reservoir easier to maintain.
Why not just make the roof?
Building a permanent roof or floating cover over a reservoir of this size would have been technically challenging and extremely expensive. According to LADWP, the cost of the Shade Ball project was approximately US$34.5 million, significantly less than the estimated cost of constructing a large engineered cover. The balls require little maintenance and can be deployed relatively quickly, making them a practical solution that meets regulatory requirements.
How were shade balls installed?
Installing the balls was surprisingly simple. Thousands of boxes containing plastic shells were delivered by truck to the reservoir. Workers released them into the water through large chutes, and the balls naturally spread to the surface. Because they float freely, they constantly rearrange themselves as wind and water movements change, ensuring consistent coverage without the need to be fixed in place.
Did plastic pollute drinking water?
No, shade balls were manufactured specifically for use in drinking water reservoirs and are made from materials approved for long-term contact with potable water. The carbon black coating also helped protect the plastic from degradation in sunlight. During their use, water quality was continuously monitored to ensure that the balls did not negatively impact the city’s drinking water supply.
What happened to shade balls?
Shade balls were never intended to be a permanent feature. As the Los Angeles Reservoir and surrounding water infrastructure were improved, including upgrades to treatment and storage systems, many of the original balls were removed. Those that had reached the end of their service life were recycled where possible, while the modern design of the reservoir reduced the need for floating covers.
A simple idea that caught the world’s attention
The image of millions of black balls floating in the reservoir initially shocked people around the world, but the project proved to be an innovative response to the many challenges facing Los Angeles. By reducing evaporation, limiting bromate formation, discouraging algae growth, and protecting water quality, shade balls demonstrate how a relatively simple engineering solution can provide significant environmental and public health benefits. This initiative remains one of the most recognizable examples of creative urban water management and continues to be studied as an example of practical, cost-effective infrastructure design.