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.
I tell you what, fill up your bath with "clean" water from you tap, plug a hair drier in to the power socket, now sit in the bath while dropping the hair drier into it. Let us know how good your theory holds up on the 220V "low voltage"
Water is an extremely efficient coolant, hence why it's used as such in so many applications. Any reference to electrical conductivity etc is by this stage immaterial, the prime objective is to cool the thing down by whatever means is available. Water is typically available and is ideal for that purpose. It's not distilled, and even if it was, it would become instantly contaminated by the time it was put to the intended use.