if you use water on a fire, what are you accomplishing that will help tackle the fire?

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.