system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are the "shade balls" that are being put in open water reservoirs in California to prevent them evaporating, black? Wouldn't something reflective or white make more sense?
gpt
The balls aren't there to prevent evaporation. They are put in place to prevent UV Rays from interacting with the chlorine and bromine in the water.  Without the balls, those 'keep clean' the water chemicals would become 'hurt the people' chemicals. 

I think this confusion comes from a misleading title on a few gif/article posts here.