Muni Metro service was halted at Montgomery Station.
The cause of the soaking was the failure of a valve in a fire-suppresion system at the Muni Metro level. That system was being tested when something went wrong at about 4:30 AM. Muni officials told reporters the valve was closed by 6 AM, but water continued to pour into the lower-level BART station for several hours.
BART employees used squeegees, mops, and vacuums to move water off the platform and eventually erected makeshift plywood shelters to shield passengers from the sheets of falling water.