Millions of black plastic balls floating in drinking water reservoirs may sound like an environmental disaster, but for Los Angeles, they’re becoming an ingenious solution to several major challenges. The unusual sight attracted worldwide attention, leaving many wondering why a city would deliberately cover its water supply with 96 million plastic balls. Far from being a publicity stunt, the Los Angeles Department of Water and Power (LADWP) introduced floating “shade balls” to conserve water, protect drinking water quality and meet strict environmental regulations during California’s severe drought. The project went on to become one of the world’s most innovative and cost-effective examples of modern water management.
What are the black balls falling into Los Angeles drinking water?
The black balls are hollow plastic balls called “shadow balls”, each about 10 centimeters (4 inches) in diameter. Made from high-density polyethylene (HDPE), a durable plastic commonly used in water pipes and baby bottles, each ball contains a small amount of water to remain stable and prevent it from blowing away in strong winds. The Los Angeles Department of Water and Power (LADWP) released all 96 million shade balls into Los Angeles reservoirs in August 2015, completing the largest shade ball project in the world at the time. The carbon black coating protects the plastic from ultraviolet (UV) radiation, giving the ball an expected service life of approximately 10 years.The Los Angeles Reservoir covers approximately 175 acres (71 hectares). Engineers calculated that approximately 96 million shade balls would be needed to cover most of the water. Rather than forming a rigid layer, the balls float freely and adjust automatically as the water level rises and falls. Together they form a protective blanket that blocks sunlight while allowing the reservoir to continue functioning normally.
Reducing evaporation during California drought
One of the main goals of the project is to conserve water. Southern California often experiences long periods of drought, with large open reservoirs losing large amounts of water to evaporation in the intense sunlight. By shading the surface, the balls reduce the amount of solar energy reaching the water’s surface, helping to minimize evaporation. LADWP estimates that the project will save approximately 300 million gallons (approximately 1.1 billion liters) of water per year, enough to supply thousands of homes each year.
Prevent bromate formation
While conserving water is important, protecting drinking water quality is even more important. Reservoirs contain naturally occurring bromide, which reacts during water treatment. When ozone is used to disinfect water, exposure to sunlight converts bromide into bromate, a chemical listed as a possible human carcinogen by the International Agency for Research on Cancer (IARC). Since California has strict limits on the amount of bromate in drinking water, blocking sunlight will significantly reduce the likelihood of this reaction occurring.
Control algae, birds and debris
Shade balls also offer some additional benefits. By reducing sunlight exposure, they limit algae growth, help maintain water quality and reduce treatment requirements. They also prevent birds from landing on the reservoir, reducing the risk of fecal contamination. Additionally, the floating layer reduces the amount of dust, leaves, and other windblown debris that enters the water, making the reservoir easier to maintain.
Why not simply build a roof?
Building a permanent roof or floating cover on a reservoir of this size is technically challenging and extremely expensive. According to LADWP, the shade ball project will cost approximately $34.5 million, well below the estimated cost of constructing a major engineering overlay. The balls also require less maintenance and can be deployed relatively quickly, making them a practical solution for meeting regulatory requirements.
How are sunshade balls installed?
Installing the ball is surprisingly easy. Thousands of boxes filled with plastic balls were trucked to the reservoir. Workers release them into the water through large chutes, where the balls naturally scatter on the surface. Because they float independently, they constantly rearrange as wind and water movement change, ensuring consistent coverage without having to be fixed in place.
Is plastic contaminating drinking water?
Won’t. Shade balls are specially manufactured for use in drinking water reservoirs and are made of materials approved for long-term contact with drinking water. Carbon black coatings also help prevent plastics from degrading in sunlight. During their use, water quality is continuously monitored to ensure the balls do not negatively impact the city’s drinking water supply.
What happened to the shadow ball?
The shade ball was never intended to be a permanent feature. As improvements were made to the Los Angeles Reservoir and surrounding water infrastructure, including upgraded treatment and storage systems, many of the original balls were removed. Those reservoirs that have reached the end of their useful life are recycled wherever possible, while the modern design of reservoirs reduces the need for floating caps.
A simple idea caught the world’s attention
The image of millions of black balls floating on a reservoir initially confused people around the world, but the project proved to be an innovative response to the multiple challenges facing Los Angeles. By reducing evaporation, limiting bromate formation, inhibiting algae growth and protecting water quality, shade balls demonstrate how a relatively simple engineering solution can deliver significant environmental and public health benefits. The initiative remains one of the best-known examples of creative urban water management and continues to be studied as an example of practical, cost-effective infrastructure design.
