The normal boiling point of water is 100 °C, 212 °F, or 373.1 K. The “normal” refers to sea level or an elevation of 0 meters or feet. But, the boiling point of water changes with elevation. The boiling point is a higher temperature below sea level and a lower temperature above sea level.
Factors That Affect the Boiling Point of Water
The boiling point of water is the temperature where the liquid’s vapor pressure equals atmospheric pressure. The reason boiling point changes with elevation is because atmospheric pressure changes. The effect is noticeable when you compare boiling point in a valley compared to a mountain top. For every 150 m (500 ft) increase in elevation, water’s boiling point decreases about half a degree Celsius or single degree Fahrenheit. But, even daily barometric pressure changes affect boiling point, although the temperature difference is too small to notice.
Atmospheric pressure isn’t the only factor that affects boiling point. Impurities increase boiling point through a process called boiling point elevation. For example, adding salt to water increases its boiling point. While some people add salt to boiling water because they think it will cook food faster at the higher temperature, the effect is really too small to make a difference.
Boiling Point in Denver, La Paz and Other Places
Water boils at a lower temperature in cities like Denver and La Paz, but at a higher temperature in places like Death Valley and the Dead Sea. If you live in a high altitude location, food cooks at a lower temperature, so it often takes longer to cook. You can’t make water hotter by boiling it longer or applying more heat. This is why many recipes include high altitude cooking directions or recommend using a pressure cooker.
| Location | Elevation | Boiling Point (°C) | Boiling Point (°F) |
| The Dead Sea | -427 m (-1401 ft) | 101.4 | 214.5 |
| Death Valley | -86 m (-282 ft) | 100.3 | 212.5 |
| Baku, Azerbaijan (lowest capitol city) | -28 m (-92 ft) | 100.1 | 212.2 |
| Sea Level | 0 m (0 ft) | 100 | 212 |
| London | 14 m (36 ft) | 99.96 | 211.9 |
| Denver | 1609 m (5280 ft) | 94.7 | 202.5 |
| La Paz, Bolivia (highest capitol city) | 3640 m (11942 ft) | 87.8 | 190.0 |
| Mt. Everest | 8848 m (29029 ft) | 69.9 | 157.8 |
Boiling Water at Room Temperature
You can boil water at room temperature if you lower the atmospheric pressure enough. You can demonstrate this for yourself using a plastic syringe. Pull up a small volume of water into the syringe, leaving lots of air space. Now, put your finger over the open end of the syringe to seal it and pull pack on the plunger as quickly as you can to lower the pressure. It might take a couple of tries to perfect your technique, but you can see the water boil. If you have access to a vacuum pump, an easier method is to apply a vacuum to a sealed container of water.
Does Water Freeze or Boil in Space?
Similarly, water immediately boils in the vacuum of space. Then, the vapor immediately crystallizes into ice. If you watch a rocket launch into space you can sometimes see ice forming on surfaces. Also, when astronauts release urine into space, it vaporizes before it forms frozen crystals.
References
- DeVoe, Howard (2000). Thermodynamics and Chemistry (1st ed.). Prentice-Hall. ISBN 0-02-328741-1.
- Goldberg, David E. (1988). 3,000 Solved Problems in Chemistry (1st ed.). McGraw-Hill. section 17.43. ISBN 0-07-023684-4.
- West, J. B. (1999). “Barometric pressures on Mt. Everest: New data and physiological significance.” Journal of Applied Physiology. 86 (3): 1062–6. doi:10.1152/jappl.1999.86.3.1062