Plastic balls used to reduce evaporation

The Los Angeles Reservoir in Sylmar was covered with 96 million plastic balls in 2015 to reduce water loss through evaporation during the California drought. The balls, each 4 inches in diameter, were designed to block sunlight and prevent algae growth, improving water quality and reducing evaporation by 85 to 90 percent.

Reservoir appearance and water savings

The reservoir, covering about 71 hectares, looked like an "immense black sheet" due to the plastic balls. The Los Angeles Water Company estimated the balls could save about 300 million gallons of water annually, equivalent to 1.1 billion liters.

Environmental cost of the balls

A 2018 study in Nature Sustainability found that producing the balls used up to 2.9 million cubic meters of water, more than the water saved over their 1.5-year operational lifespan. The study highlighted that the water used in producing the balls came from upstream processes involving oil, natural gas, and electricity.

Long-term effectiveness and sustainability

The study noted that the balls would take about 2.5 years to repay their water debt under continued drought conditions. Outside of droughts, the balls would need to stay in place longer to achieve similar water savings, making their effectiveness context-dependent.

Expert opinion and alternative methods

Dr. Kaveh Madani of Imperial College London emphasized the need to balance the benefits of the balls with their environmental costs. A 2014 study found that mandatory water restrictions, like stopping lawn watering, were more effective than plastic balls in saving water.

Previous testing and manufacturer claims

The Los Angeles Water Company had tested a similar approach in 2009 with 3 million balls on the Ivanhoe Reservoir. The ball manufacturers claimed a potential lifespan of up to 25 years, suggesting the initial water debt could be repaid over time if the balls remained in use.