The covering of the reservoir surface is expected to save about 300 million gallons of water every year, according to NPR, and is part of California's latest attempt to avoid worsening its ongoing four-year drought. The total cost for the deployment of the shadeballs amounts to $34.5 million.
According to Bloomberg, the four-inch-wide shadeballs are coated with a UV-light blocking chemical. They're hollow and filled with water to keep them from flying away. Each one costs around 36¢ to make. Sydney Chase, the CEO of XavierC, a company that specializes in the manufacture of those balls, told Bloomberg that she calls them "conservation balls" as they help keep water bodies clean and preserve water. The balls can also be used in reverse, when distributed on toxic waters in order to keep animals out. The balls are also designed not to degrade and are expected to last 10 years before being recycled.
The Los Angeles Reservoir is the latest body of water to be filled with 'shadeballs.' Three others are already filled with the floating devices. The shadeball mania started in 2008 after Los Angeles realized that two of its reservoirs had unusually high levels of bromate, a suspect cancer-causing agent. Since bromate is formed when sunlight reacts with bromide (a chemical found in water) and ozone or chlorine (both of which are used to disinfect water) the city decided to shield the water from sunlight. The 'shadeballs' were the most convenient and cheapest option and were introduced to the Ivanhoe reservoir in 2008.
Tasch, Barbara, firstname.lastname@example.org, Business Insider, http://www.msn.com/en-us/news/us/why-96-million-shadeballs-were-just-released-into-the-la-reservoir/ar-BBlGPlw?ocid=HPCDHP, August 13, 2015