Ball Pit?

To protect its drinking water, Los Angeles, California, dumped 96 million floating, plastic balls into a 175-acre reservoir. The black “shade balls” reflect the sun’s high-powered ultraviolet (UV) rays. These rays can react with a naturally occurring chemical in water, called bromide, turning it into bromate. Bromate is a suspected human carcinogen—a substance that causes cancer.

The balls not only ensure that the water citizens depend on doesn’t become contaminated with a potentially hazardous chemical, they also reduce evaporation. Sun shining on the water causes it to heat up and change from a liquid to a gas. The plastic balls slow this process and could save an estimated 300 million gallons of water each year—enough to serve 2,760 homes.