# video | Why in the reservoir of Los Angeles poured 96 million black balls?

Recently, the department of water and energyLos Angeles (Los Angeles Department Water & Power - LADWP) fitted several large trucks filled with 96,000,000 (ninety-six million) plastic black balls to one of the local reservoirs. Once on the water surface, from afar, they look at the oil slick, but in fact perform a very useful function. And despite the very common opinion that these balls are used to reduce the level of evaporation of fresh water from reservoirs, they are intended for a completely different purpose. So why are they?

LADWP on duty concerned about qualitydrinking water in the metropolis uses them to prevent the appearance in the drinking water of dangerous carcinogenic (can provoke the development of cancer) compounds - bromates. The increase in the concentration of these substances in water is explained by three factors: the presence of bromides, which are naturally present in groundwater, chlorine, used for water disinfection, and sunlight. It is the bright Californian sun playing such a cruel joke with the reservoirs: it starts the reaction of bromate synthesis. Because experts and suggested to close the water from the light.

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Using a flexible solid coating wouldtoo expensive, and the metal roof also would have required a lot of time for installation. The idea to use the black balls Bird Ball (“Bird Balls”) came to LADWP biologist Brian White many years ago. And since then LADWP uses only them.

The balls themselves are made of polyethylene foodlevel and high density with additives, have a size of 10 centimeters and are filled with 210 milliliters of water. Previously, the water was not used, but in Los Angeles there are quite strong winds, so that the balls were not blown off from the water surface (they used to weigh only 40 grams) they were partially filled with water. They are not afraid of heating to 80 degrees Celsius, they are not afraid of frost. And sunlight does not cause the degradation of the polymer constituting the balls. Black, because in this way they block all the sunlight that triggers the chemical reaction of the formation of bromates. In addition, they use a special black dye, which is considered safe for contact with drinking water. Thanks to this combination, the balls can be reused under direct sunlight for at least 10 years.

Several companies produce balls in differentvariations. "Bird" they are called because they are used to close the surface of water bodies and wetlands located near airports. The ponds covered with such balls are not interested in birds. Birds just do not see disguised lakes from the air. This means that the skies in the vicinity of the runways are freer.

Another useful feature of the balls isthat they drastically reduce the oxygen saturation of water, suppressing algae reproduction. Even the balls are able to lower the point where ice begins to form in the open pond in winter by several degrees. And they significantly reduce the loss of heat by the reservoir.

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