The chemical bromate, is craeted when bromine in groundwater is combined with chlorine, and exposed to sunlight. It is said to be the first time an occurrence like this has been observed. Bromine is a key ingredient in flame retardants, so the chemicals used to fight the California fires may be leeching into the ground water. The dams are a fraction of LA's total water storage, but fire retardant chemicals would have been used over a wide area of California State, so soils may have unusually high bromine levels. It may pay to find out exactly why this happened to be wary of where it may happen again.