When you throw water on most ordinary fires, you’re mainly cooling the burning material so it can’t stay hot enough to keep burning.

What water actually does

  • It absorbs a huge amount of heat as it warms up and then turns into steam, dragging energy out of the flames and fuel.
  • As it turns to steam, the expanding water vapor helps push away some of the nearby air, which slightly reduces the oxygen right at the flame’s surface.
  • The cooler, wet surface left behind makes it harder for the fire to re‑ignite, because the material has dropped below its ignition temperature.

Fire triangle link

Fire needs three things: heat, fuel, and oxygen (the “fire triangle”).

  • Water attacks the heat side by cooling the fire drastically.
  • In some situations (like enclosed spaces or heavy steam production), it also partly interferes with the oxygen side by displacing air at the flame front.

So, if you use water on a suitable type of fire, you are mainly accomplishing powerful cooling of the burning material, and sometimes a bit of smothering, which together help tackle and eventually put out the fire.

TL;DR: You’re pulling heat out of the fire and, to a lesser degree, crowding out the oxygen right where the flames are, so the combustion process can’t keep going.