The boiling point of water depends on the atmospheric pressure, which changes according to elevation. The boiling point of water is 100°C or 212°F at 1 atmosphere of pressure (sea level), but water boils at a lower temperature as you gain altitude (e.g., on a mountain) and boils at a higher temperature if you increase atmospheric pressure.

The boiling point of water also depends on the purity of the water. Water which contains impurities (such as salted water) boils at a higher temperature than pure water. This phenomenon is called boiling point elevation, which is one of the colligative properties of matter.