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California’s latest water preservation strategy? Ninety-six million small black plastic balls, the last of which were dropped into the Los Angeles Reservoir in August.
“Left unchecked, sunlight can promote algae growth in the water,” explains Richard Harasick, director of water operations at the Los Angeles Department of Water and Power. “When this mixes with the chlorine disinfectant we use, it causes the formation of carcinogenic by-products.”
By covering the surface to prevent sunlight reaching the water, the balls not only halt algae growth, they also stop evaporative loss of up to 1.1 billion litres of water a year. “This is our largest reservoir, which makes it particularly difficult to cover,” says Harasick. “A floating cover would have been very expensive.” The 10cm-wide plastic balls cost just 36 cents (23p) each, with a total cost of $34.5 million — a saving of more than $250 million.
The idea to use the balls came from seeing them used to prevent birds drinking from contaminated ponds. The carbon that gives them their colour will prevent degradation by UV rays, trebling the plastic’s life span. “This reservoir will have these balls for at least a decade,” Harasick says. “Then they’ll be replaced with new ones.”