What is the boiling point of water?
At sea level, pure water boils at 100°C (212°F). The boiling point drops at higher altitudes, where air pressure is lower, and rises when salt is dissolved in it.
Water boils when its vapor pressure equals the pressure of the air above it. At sea level, the standard air pressure is 1 atmosphere, and that happens at 100°C. The Celsius scale was originally based on this point and on the freezing point of water.
Air pressure falls as you climb, so water boils at lower temperatures. In Denver, about 1,600 meters up, water boils at about 95°C (203°F). On the summit of Mount Everest it boils at only about 70°C (158°F), which makes cooking pasta or rice there very slow.
Pressure cookers and salt
A pressure cooker traps steam and raises the pressure inside, so water can reach about 120°C before boiling. Food cooks much faster. Adding salt raises the boiling point slightly, but the amount used in cooking changes it by less than one degree, so it mainly affects flavor.
Did You Know?
Water can be heated above its boiling point without bubbling in a very smooth container, especially in a microwave. This superheated water can suddenly erupt when disturbed, so it is best to heat water carefully.