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Why there are plastic shade balls on Los Angeles Reservoir

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The Silver Lake Reservoir Complex in Los Angeles, California, contain two reservoirs provides water for 600,00 homes in Los Angeles area. In 2007 it was announced that the reservoir had contaminated with unusually high levels of the cancer-causing chemical bromate. The reservoirs were immediately isolated and drained over several weeks and then refilled.

In 2015, 96 million “shade balls” were dumped into the Los Angeles Reservoir to improve water quality and save water. The shade balls originally used to prevent chemical treatments in the reservoir from reacting with sunlight and creating bromate, which is carcinogenic. California began deploying shade balls as a cost-effective way to reduce bromate levels and prevent algae growth.

At the time, Californians faced one of the historically worst droughts, and conserving water was on everyone’s minds. The shade balls could keep contaminants out of the water and reduce the evaporation of the reservoir by 85 to 90 percent during a drought. The officials said the annual savings could amount to up to 300 million gallons of water, enough to supply drinking water to 8,100 people.

What are shade balls?

Shade balls are made from high-density plastic. They are black, and about 10 inches in diameter. They are designed to reduce evaporation by 80 to 90 percent by providing shade from the sun. Originally shade balls were used to keep birds away from toxic tailing ponds near mining sites. After that, airport used them to keep birds away from airport runways by covering nearby ponds and rivers. Then the balls were known as bird balls

Pros and Cons of using shade balls

  • shade balls would need to stay on the Los Angeles Reservoir for at least a year or more to save water. It could take up to 2.5 years to recover the water used.
  • Since shade balls have stayed on the Los Angeles Reservoir more than six years now, they are likely now starting to save more water than they cost to produce.
  • The reservoir managers plan to keep shade balls as a permanent solution to water quality issues on the Los Angeles, replacing them every 10 years.
  • With expected results achieved they have deployed shade balls at three other reservoirs, between 2008 and 2012, where they stayed temporarily for five to nine years.
  • During no-drought periods water saving is less because of less evaporation when the air is not as dry.
  • The water saved from evaporation by shade balls is small compared to other water-saving strategies such as not irrigating lawns.
  • The balls have been successful in both reducing the creation of toxic bromate and reducing algae growth in public reservoirs.
  • There is a chance that BPA chemicals from shade balls could be leaching into the waters of the reservoir. Typically found in plastic, BPA is an endocrine disruptor that usually breaks down in water after a few weeks or months.

In the end, it seems as though shade balls have been removed from all but one of LA’s reservoirs. According to sources this removal was mostly due to the cost-prohibitive nature of the shade balls project, not the environmental or health concerns surrounding their usage. It remains to be seen what long-term effects the balls will continue to have on the quality of LA’s drinking water.





Nimal C. Jayasundara
Nimal C. Jayasundara
Ph.D., PE. Water Resources Engineer, California Department of Water Resources, California.


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