Why does water boil at high altitudes at lower temperatures?

Water boils at lower temperatures on mountains because air pressure is weaker up high.

Imagine you're blowing up a balloon. The more air you blow in, the tighter it gets, that’s like pressure. At sea level, the air is thick and heavy, pushing down on everything, including water. But when you go up a mountain, there's less air above you, so the pressure is lighter, like blowing only a little into the balloon.

When water boils, it’s trying to escape as steam. Think of it like kids wanting to jump out of a swimming pool, they need enough push from below to get up and out. At lower pressures, it's easier for water to turn into steam, so it doesn’t need to be as hot.

At sea level, water boils at 100°C (212°F), but on top of a mountain, where the air is thinner, it might only need about 90°C (194°F) to start boiling, just like kids needing less push to jump out of the pool when there are fewer people in it!