Los Angeles shade balls: 96 million spheres, 11 years on

A chemical problem, not just evaporation

The project became famous as an anti-evaporation measure, but its main goal was chemical. Sunlight helps turn bromide in the water into bromate, a potentially carcinogenic byproduct whose level in drinking water is regulated. The balls block about 95% of sunlight, slow algae growth and reduce the need for chlorine.

Each sphere is about ten centimetres wide and made of high-density polyethylene suitable for drinking water. Carbon black gives it its colour and protects it from ultraviolet radiation, and water inside keeps the wind from moving it. The alternative, floating covers over a divided reservoir, was budgeted at no less than $300 million. Los Angeles had already tested the idea at Ivanhoe in 2008.

The bill nobody saw from the shore

A study published in Nature in July 2018 by researchers from MIT, Imperial College London and the University of Twente added the water footprint of making the balls. Their estimate ranged from about 250 million to 2.9 billion litres. In the reference scenario, manufacturing needed around 2.9 million cubic metres of water, against estimated savings of 1.7 million cubic metres during the drought period studied. The system would need about two and a half years to repay that debt, and longer outside dry periods when evaporation is lower.

The authors did not call the balls useless. They showed that their environmental value depends on accounting well beyond the reservoir itself.

What happens now

The Los Angeles Department of Water and Power has warned that the balls can lose structural integrity, split at the seams or break, and said they would be removed, recycled and replaced over time. No confirmed figures exist on how many have deteriorated or been replaced, or whether there is an updated renewal schedule. Nor is there official word on whether the city will move to another system, such as floating solar panels. Its documents still present the balls as a water-quality measure alongside ultraviolet disinfection.