Water is actually one of the best fire extinguishers also for low voltage installations. Clean water will not conduct low voltages and water is one of the best substances to cool down the burning material. The water vapor will be about 1600x the water volume and efficiently replace oxygen.
Polluted water and salt water CAN conduct even low voltages like 220V, so make sure the water is clean. Never use water on burning liquids or high voltage installations.