Los Angeles’ solution to shielding its reservoirs is shade balls

Covering 36,000 acre feet of water in reservoir isn’t easy. Pool covers don’t really come in those sizes, and even if they did, costs and difficulties of buying and maintaining a tarp that big are prohibitive for most cities. Chemistry (and the thus, the Environmental Protection Agency) doesn’t care about the practicalities tarp ownership though (mostly), creating a demand for a new approach at covering municipal water supplies. The solution seems to be shade balls.

Shade balls are hollow, plastic balls that act as a modular tarp-substitute. 96 million balls have been poured across the surface of all the reservoirs in Los Angeles, where they form a protective layer to block the sun from hitting the water directly. Each ball is very cheap to produce, but is expected to last 10 years before needing replacement. Unlike a tarp, damaged areas are much less of a concern, since other balls can immediately roll into any openings, letting the ball-layer “heal” itself.

Bromate blocking balls

There’s more to this project than engineering novelties, of course. Blocking sunlight prevents naturally-occurring bromide in the water from reacting with chlorine added for water treatment purposes, avoiding the creation of bromate, a carcinogen. The balls also reduce algae growth and evaporation. With California in its eighth year of drought, making the most of every drop of water is a strong motivator.

My first grader asked: Is it really ok to be putting all this plastic in the water? While the balls shouldn’t be leeching anything like BPA into the water supply, my daughter’s concern was more about the amount of garbage being dumped in the ocean. Fortunately, the shade balls aren’t being added arbitrarily to waterways that lead to the sea. Outside of worries about choking sea turtles, it would be a waste of valuable shade balls to let them trickle away. They’re being concentrated in controlled reservoirs, where they can later be scooped up and replaced as needed.

Source: LA Rolls Out Water-Saving 'Shade Balls' by Laura Wagner, The two-way