In the Delta, bromide is a naturally occurring constituent found in the water that, along with organic carbon, are precursors to the formation of harmful disinfection byproducts in municipal water supplies.. Water containing high amounts of bromide requires additional costly treatment as there is a health risk from exposure to disinfection byproducts.
Nearly all bromide found in the Delta’s water comes from seawater intrusion. Concentrations of bromide in the Delta vary seasonally with the lowest bromide concentrations associated with the highest river flows because seawater intrusion is lowest during periods of high outflow.
Delta water is higher in bromide as compared to other sources, and since there are no significant sources of bromide in the watershed, controlling bromide is not possible. However, changing disinfection processes for municipal water supplies to ozone or chloramine disinfection processes reduces formation of harmful disinfection byproducts.
For more on bromide:
Drinking Water Quality: Bromide, document from CALFED via the Delta Stewardship Council