Caused by a garden hose
"...A garden hose had been overflowing the pool above the hillside for an “unknown amount of time” when it caused the flooding and subsequent collapse, according to the Fire Department, which drained the pool. It was then red-tagged by the L.A. Department of Building and Safety, along with portions of a damaged structure — a vacated commercial building, Lantz said — at the base of the hill. ..."