Shade ball

A shade ball is a small plastic sphere floated on top of a reservoir for environmental reasons, including to slow evaporation and prevent sunlight from causing reactions among chemical compounds present in the water.

[3] Starting in mid-2009, the Los Angeles Department of Water and Power (LADWP) put about 400,000 balls in the Ivanhoe reservoir with the main objective of preventing the formation of a carcinogenic chemical, bromate, which forms when sunlight interacts with naturally occurring bromine and the chlorine added to prevent algae growth.

[1] In 2014 and 2015, the LADWP put 96 million shade balls onto its largest reservoir (Las Virgenes)[5] in response to the United States Environmental Protection Agency's surface water treatment rule,[6] which requires large reservoirs of treated water to be covered.

[9] The balls saved 1.7 million cubic metres of water from evaporating during their deployment from August 2015 to March 2017.

[10] The shade balls used in the Los Angeles project are made of high-density polyethylene (HDPE) with carbon black additive to protect the plastic from ultraviolet radiation.