If you've seen a video about California reservoirs or even visited one, you might have glimpsed a layer of black balls floating on the surface; these balls, made from high-density polyethylene, are known as shade balls, and are designed to decrease bromate levels and prevent algae growth. They cost about $0.36 each and are a cost-effective way to save the environment.

In 2008, Los Angeles successfully deployed 400,000 shade balls in the Ivanhoe Reservoir, and in 2015, it dumped 96 million shade balls into a 175-acre reservoir that had enough drinking water to supply the entire city for up to three weeks. At the time, California was experiencing an historic drought, and the balls were projected to save up to 300 million gallons of water.

Shade balls seem like a win-win, but researchers determined that producing the balls could use more water than they save. Although the balls could save 1.15 million cubic meters annually, the manufacturing process takes up to 2.9 million cubic meters of water. Shade ball manufacturers point out that their balls should last 25 years; with time, these water losses could be offset.