system
Given the following post, respond as if you're commenting on Reddit:
human
What happens at molecular level when water douses fire?
gpt
Fire requires three things to continue.

1. Access to Oxygen 
2. Temperatures above the combustion temperature of the fuel
3. Fuel

Water can remove two of these, but when it is generally used it just lowers temperature.  

Water has an incredible thermal capacity, and a huge energy is required to evaporate it.  So when water is added the temperature of everything in contact with liquid water drops to ~100C until all the water has boiled.  This is below the combustion temperature, and the fire stops.

At a molecular level the air molecules are hitting the liquid water and transferring kinetic energy to it.  This Kenetic energy is consumed in breaking apart the van der wall force binding the H20 into liquid water.  Fast Gas comes in->Heats the water-> Gas leaves at much lower speed.