A truck dumps tens of thousands of 'shadow balls' into a water tank in Los Angeles, California. The water distribution company “Las Virgenes Water District” uses these black polyethylene balls about 10 cm in diameter, in order to block the UV rays of the Sun, limiting a chemical reaction that converts the bromine in carcinogenic bromate and the water evaporation process. The balls also keep away birds and stop the proliferation of algae. It took loads more to cover the entire surface of the tank.