system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:why is water best for putting out a fire? is it the physical nature or the chemical nature of water which is more important?
gpt
Water is best for putting out *certain types* of fires. Others, it's horrible for. Since the most common types of fires have to do with wood and plastics burning, it's generally the first thing that comes to mind as an extinguisher.

How it works is through a number of means, and they have more to do with heat and physical properties than with chemical reactions.

- It steals a LOT of heat from the area, both because the water itself is much much cooler than the combustion temperature of most wood-based fires, and because it takes a tremendous amount of energy for it to instantly convert to steam and leave the area of the fire. This massive drain is why kettles take so long to boil dry even after they reach boiling point.

- It splashes over and immediately places a film on the area it's applied to. This film cuts off access to air, and the oxygen that's in that air, reducing the fire's access to that oxygen.

- As water is a liquid that absorbs into porous stuff quite easily, it immediately soaks into porous substances, helping to extinguish the fire at the material's core (such as the black porous coals in a campfire)

Why it's bad for some fires is because it can splash around the components of some dangerous fires, such as burning grease or oil. They don't dissolve in water and burn at very high temperatures, so the water hitting them actually can explode into scalding steam, and the force of that explosion can spread the inflammable liquid, and the fire itself, even further. This is why you should never throw water on a grease fire.