Shade balls are small, black, polyethylene spheres designed to float on the surface of large water bodies, primarily reservoirs. These four-inch diameter orbs are partially filled with water to ensure they remain in place even under windy conditions. Their primary function is to cover vast expanses of water for environmental and water quality purposes.
Reducing Water Evaporation
Shade balls significantly reduce water evaporation from reservoirs. Their design addresses sunlight and wind, the two primary factors contributing to evaporation. The black high-density polyethylene (HDPE) spheres absorb solar radiation, preventing water heating. This reduction in water temperature slows molecular activity, thereby decreasing the rate at which water molecules escape into the atmosphere as vapor.
The physical barrier created by millions of floating balls also minimizes the water’s exposure to wind. Wind currents can carry away water vapor from the surface, accelerating evaporation. The interconnected layer of shade balls disrupts air movement above the water, forming an insulating layer that traps humidity. This combined action leads to substantial water savings, particularly in arid regions experiencing drought conditions.
Protecting Water Quality
Shade balls also protect and improve water quality. A significant benefit is their ability to inhibit algae growth, which thrives in warm, sunlit water through photosynthesis. By blocking nearly all sunlight, the spheres create an unfavorable environment for algal proliferation, reducing the need for chemical treatments.
They also mitigate harmful chemical reactions in sun-exposed water, such as bromate formation. Bromate, a suspected human carcinogen, forms when naturally occurring bromide reacts with chlorine in sunlight. The black spheres effectively block the ultraviolet (UV) radiation that catalyzes this reaction, minimizing bromate levels in treated drinking water. Additionally, this physical cover acts as a barrier against airborne contaminants like dust, debris, and pollutants, and deters wildlife, helping prevent contamination from animal waste.
Real-World Applications
Shade balls have found prominent real-world application, notably in the Los Angeles Department of Water and Power (LADWP) reservoir project. In 2008, LADWP began deploying them in reservoirs like Ivanhoe, primarily to prevent bromate formation. The largest deployment, approximately 96 million shade balls, occurred in 2015 on the Los Angeles Reservoir.
This large-scale deployment responded to severe drought conditions and federal water quality regulations, including the United States Environmental Protection Agency’s (EPA) Long Term 2 Enhanced Surface Water Treatment Rule, which requires large reservoirs of treated water to be covered. Shade balls offered a cost-effective alternative to more expensive solutions. LADWP estimated this initiative would save hundreds of millions of gallons of water annually while maintaining water quality compliance.
Broader Implications
Shade balls have broader implications beyond their immediate functional benefits. They are made from high-density polyethylene (HDPE), a durable, UV-resistant plastic often with carbon black added to enhance UV protection. HDPE is non-toxic and commonly used for food and beverage containers, making it suitable for drinking water contact.
Their lifespan is estimated at 10 to 25 years before they need replacement. At the end of service, the HDPE material is recyclable, which helps manage their environmental footprint. However, manufacturing millions of these balls requires energy and water, prompting discussions about their overall water and energy balance. The logistics of eventual removal, recycling, or replacement are considerations for long-term reservoir management.