In a move that captured global attention, the Los Angeles Department of Water and Power (LADWP) deployed 96 million black plastic “shade balls” into the Los Angeles Reservoir in 2015. This unconventional infrastructure project was designed to protect the city’s drinking water supply from sunlight-induced chemical reactions, animal contamination, and evaporation during a period of extreme drought.
The Science Behind the Shade
The primary driver for the deployment was the mitigation of bromate formation. When sunlight interacts with bromide and chlorine—substances naturally present in the water—the byproduct bromate is created, which is a suspected carcinogen.
By covering the surface of the 175-acre reservoir, the balls effectively blocked ultraviolet light. This simple physical barrier prevented the chemical transformation, ensuring that the water met stringent state and federal public health standards without the need for an expensive, energy-intensive chemical treatment plant.
Water Conservation and Environmental Impact
Beyond chemical safety, the shade balls served as a critical tool for water conservation. At the time of their installation, California was grappling with a historic multi-year drought that threatened the city’s water security.
The balls acted as a thermal shield, significantly reducing water evaporation. According to LADWP officials, the project saved approximately 300 million gallons of water annually, providing a tangible buffer against the impacts of a warming climate.
Expert Analysis and Industry Perspectives
Environmental engineers have noted that while the shade balls were highly effective for the Los Angeles Reservoir, the solution is not a universal fix. Dr. Brian White, a retired LADWP biologist who championed the project, noted that the balls were specifically chosen because they provided a cost-effective alternative to building a multi-million dollar water filtration facility.
Critics, however, have pointed toward the environmental footprint of manufacturing millions of high-density polyethylene plastic spheres. The production process requires oil extraction and manufacturing energy, leading to debates about whether the long-term environmental benefits of water preservation outweigh the initial ecological cost of the plastic production.
The Future of Reservoir Management
As municipalities across the globe face increasing pressure from climate change and aging infrastructure, the Los Angeles experiment remains a primary case study in low-tech, high-impact engineering. While the shade balls were intended as a temporary measure, their longevity has surprised many.
Looking ahead, the industry is watching how these reservoirs transition toward permanent covering solutions. Many cities are now exploring floating solar arrays, which offer the dual benefits of shading the water to prevent evaporation and generating renewable electricity. Whether through shade balls or solar panels, the shift toward active reservoir management is expected to accelerate as water scarcity becomes a central pillar of urban planning in the coming decades.
