There were water storage tanks in the hills in the Palisades area that were filled specifically for firefighting, but since air support on the fire was impossible for the first ~12 hours due to high winds, the fires simply spread so fast that the tanks ran empty after about five hours of water being drawn from them at something like 3-4x the normal rate, and the municipal water system in the area was never intended to be able to supply that kind of demand for the better part of a day, so refilling the tanks was difficult.
I was actually flying into LAX as the Palisades fire was starting to get bad, and even from several miles away in a moving airplane, it was possible to see the line of flames visibly moving because the wind was driving it that fast, so emergency crews never really had a chance against something like that.