The Twofold Benefits of Los Angeles’ “Conservation Balls”


The Los Angeles Power and Water Department’s (“PWD”) recent release of 96 million, black “conservation balls” into the Los Angeles Reservoir attracted global media attention. The conservation balls are four inches in diameter, hollow, made of polyethylene, and coated in a carbon substance. For the most recent project, Los Angeles paid $0.36 per ball. The balls are halfway filled with water, which allows them to float on the reservoir’s surface and form into a reservoir cover. Conservation balls are not a new or novel idea. Conservation balls have been available for at least twenty years.

The balls serve two, specific purposes for Los Angeles. First, the conservation balls increase water quality. Los Angeles has been plagued with poor reservoir water quality for decades. The balls prevent the formation of harmful microorganisms, algae, and carcinogens by blocking ultraviolet ray penetration. Second, the conservation balls prevent evaporation.


Cities, like Los Angeles, are implementing projects to cover reservoirs as means to promote public health and safe drinking water. Along with municipally imposed regulations, national regulations have also brought increased pressure to cover reservoirs. The Environmental Protection Agency’s (“EPA”) Long Term 2 Enhanced Surface Water Treatment Rule mandated either the covering of all new reservoirs that service at least 10,000 people and (2) existing reservoirs, or that the reservoirs must adhere to stricter contaminant regulations. Previous outbreaks of typhoid and cholera throughout history show that protecting reservoir water is a social imperative. Recently recognized threats to water quality, such as Cryptosporidium, have reinvigorated the push for safer drinking water. More commonly, reservoir water quality suffers from contamination of animal feces, animal carcasses, invasive species, rogue citizens defiling the water, and everyday trash buildup. Conservation balls have been utilized to protect water quality and keep wildlife off the surface water. San Francisco International Airport, London Heathrow International Airport, and the United States Air Force have all used conservation balls to deter birds from surrounding waterways.

Water quality concerns have beset Los Angeles for decades. A 2009 report, co-authored by Environmental Working Group senior scientist Olga Naidenko, ranked Los Angeles as having the 83rd best water quality amongst large, American cities. Recent news reports showed black and yellow tinted water spouting from Los Angeles area taps. The Natural Resources Defense Council stated that Los Angeles area water is “threatened by runoff and industrial or sewage contamination.”

Los Angeles historically has been slow to make improvements to its reservoirs. The state of California first recommended to Los Angeles to cover its reservoirs in 1974. In 1988, Los Angeles formed proposals to cover some of its reservoirs, including the Elysian Reservoir. The proposed covers were made of aluminum or rubber. Following the state’s push to cover the reservoirs, few Los Angeles reservoirs were ever covered. This past inattention to water quality issues may have contributed to the issues facing Los Angeles area reservoirs today.

By 1991, PWD described the Stone Canyon Open Reservoirs and Silver Lake Reservoir Complex as having deteriorating water quality, high coliform bacteria levels, and high algae counts. In 2008, the Elysian Reservoir, a reservoir that Los Angeles failed to cover in 1988, after displayed bromate contaminants and was subsequently drained. Bromate is a suspected carcinogen, and the EPA places strict limits on its presence in drinking water. Following the 2008 draining of Elysian Reservoir, PWD used conservation balls for the first time when it dumped 400,000 balls into the Ivanhoe Reservoir. The conservation balls’ primary purpose, at the time, was to increase water quality by shielding the water from sunlight, hindering the growth of algae.

Conservation balls are potentially an appropriate remedy to the unique difficulties facing Los Angeles’ water quality issues. The conservation balls protect against the formation of harmful carcinogens, microorganisms, and algae, along with hindering the presence of animals and surface debris. The pollution generated by a city the size of Los Angeles, coupled with the push back against reservoir covers and other quality control methods have had negative, long-term effects on the cities’ water quality. Despite these hurdles, Los Angeles met the EPA’s 2013 drinking water standards. However in the future, EPA standards will only continue to tighten and Los Angeles will continue to face water quality challenge. The conservation balls have the potential to benefit Los Angeles water quality in a cost effective and minimally invasive fashion. If this most recent drop of conservation balls proves successful, conversation balls may play a larger role in securing the future of Los Angeles water quality.


Although Los Angeles initially used conservation balls to protect water quality, the PWD has now embraced the balls as an evaporation suppressant. Large surface areas make reservoirs a liability in water storage, vulnerable to massive amounts of evaporation. The two most common ways to combat surface evaporation are with floating or suspended covers. Both provide similar evaporation relief and are effective in different ways. Floating covers were historically most effective at covering small areas, where the surface is easy to cover fully. Floating covers are also cheaper. Suspended covers can be prohibitively expensive, especially when needed to cover large areas.

The United States Department of Energy encourages the use of a floating cover on family swimming pools to reduce evaporation. To cover the Los Angeles Reservoir with a floating cover presents a much greater challenge than covering a swimming pool. Reservoirs the size of the Los Angeles Reservoir require cost-effective floating covers. To be cost-effective, a cover must need minimal maintenance, can be easily removed, and conform to large water surfaces without losing its shape.

Scientists have long sought a way to place an artificial protective layer over water surfaces in order to reduce evaporation. In 1917, Irving Langmuir studied how oil films on top of a liquid surface can protect against evaporation. Academics wrote extensively about these oil films, monolayers throughout the 1960s. In 2014, Wichita Falls, Texas tested a monolayer product on Lake Arrowhead. The 2.6 month test prevented 3,400,00m³ of water from evaporating, saving the city $1,700,000. However, the product required frequent application, suffered damage in the wind, and did not provide uniform coverage.

While some researchers focus on monolayers, others have researched plastic meshes, rubber mats, and interlocking hexagonal structures. Conservation balls have emerged as an alternative to monolayers and other forms of floating covers. While monolayers may be more aesthetically pleasing, conservation balls require less maintenance, are more effective against ultraviolet rays, and do not stick to the banks of open water storage areas. Conservation balls are unique in their practicality for large areas. Before, covering large reservoirs was a complex, engineering project. Now, the self-positioning balls are simply dumped into a reservoir. The balls cling to the surface, do not blow away, and do not require complex engineering, which makes them a cost effective measure. Conservation balls also protect water quality in ways that monolayers cannot. Conservation balls block out ultraviolet rays that can have damaging effects on water quality.

Los Angeles area reservoirs suffer more use, higher temperatures, and are much larger than many other reservoirs. Traditional methods of reducing evaporation, such as solid mats or earthen covers are not feasible for Los Angeles reservoirs for a variety of reasons, from being cost prohibitive to being engineering impossibility. Large floating mats often fold over themselves, a large fold in a Los Angeles Reservoir cover would be problematic to fix. Conservation balls solve this problem by dispersing themselves around the reservoir. Furthermore, conservation balls are made of polyethylene. Polyethylene is commonly used to prevent evaporation. Polyethylene shade covers can reduce evaporation loss up to 85%, and prevent algal growth. Polyethylene shade covers are suspended covers, and do not float like the conservation balls.

Polyethylene is widely considered the best material to suppress evaporation. A number of conservation ball manufacturers claim that their product prevents evaporation loss by 90%. Despite the lack of academic studies focusing on the evaporation reduction from polyethylene formed into a ball, surfaces covered with polyethylene in a variety of forms substantially lowers evaporation rates compared with uncovered surfaces. This holds true even for only partially covered surfaces. While conservation balls limit evaporation, one noted flaw of the conservation ball is how it’s round shape. Surface covers that leave one large area exposed are more successful at suppressing evaporation than covers with many small holes. The balls naturally create spaces in between each other due to the spherical shape; this in turn causes higher levels of evaporation than a solid cover that does not cover an entire surface.

Los Angeles is the first major city to use this product. How the city fares with this investment will provide significant evaporation reduction information to other cities with similar problems.


Los Angeles’ use of conservation balls is an example of a city using an innovative, relatively unknown, and relatively inexpensive product as a solution to an otherwise cripplingly expensive infrastructure project. Like any new public works project there has been scrutiny over the project and questions regarding why municipalities were not using this product sooner. To some naysayers this solution is another waste of taxpayer dollars, while others within the media and California view this project as having great potential.

However, this project by the PWD shows how small investments can have potentially long-term payoffs that prevent later environmental and political fallout. Covering a reservoir in conservation balls is a lot cheaper, in the short and long-term, than constructing a new, underground reservoir. Mayor Eric Garcetti hailed the conservation balls as saving both taxpayers and drinking water. The day may come when Los Angeles and California, as a whole, have to create solutions to challenges regarding their water systems that require much more complex answers than conservation balls. To know what role the conservation balls may play in solving future challenges, the true savings and benefits of this project must be known, not just the projected benefits. Los Angeles estimates that the balls will save 300 million gallons of water a year. Time will tell how accurate those estimates are. If this project is successful then it potentially could model for other cities across the world.

Department of Water and Power workers release the final 20,000 of 96 million black shade balls during a news conference at the Los Angeles Reservoir on Aug. 10, 2015. Photo by Gene Blevins/LA DailyNews.


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