"It's a very unusual set of factors," DWP General Manager David Nahai said. "Sunlight, mixed with chlorine together with high levels of bromide in well water that seeped into the reservoir."
The Department of Water and Power said it immediately took the reservoirs out of service when the chemical was detected in October but it didn't disclose the information to the public until Friday.
State health officials said the danger to those who drink water from the reservoirs is minimal. But some city officials are upset that the public wasn't told about the problem earlier.
"It was a great response by the DWP to take water offline," L.A. City Councilman Eric Garcetti said. "But I was disappointed we didn't hear about this. I found out about this almost a month and a half after that water supply was cut off."
"They probably should have made the public aware of the problem sooner," Silverlake resident Andrew Shinn said. "Even if there's nothing to panic about, we can at least take precautions."
The reservoirs supply tap water to about 600,000 Los Angeles residents but officials say the closures haven't left the city short of drinking water.
Both reservoirs will be emptied in January or February, cleaned and then refilled.
"The water will be used for non-potable purposes," Nahai said.
Considering the drought, officials hope all this water doesn't go to waste.
