Different boiling points of water?
Posted: Sat Jan 15, 2005 7:51 am
Why does tap water boil faster than distilled or bottled water?
In my experience you would usually see the opposite effect. Usually the distilled or bottled water would boil faster than the tap water. The reason for this is what is called boiling point elevation. Boiling point elevation occurs when there are dissolved minerals in the water. Distilled water usually has some of the mineral impurities removed and so you would expect it to boil at exactly 100 degrees C. Tap water is more likely to have dissolved minerals, unless you have some sort of water purifier attached to your tap that can remove them. Therefore, normal tap water should boil at a higher temperature than distilled water.
There are several websites you can check out to learn more about boiling point elevation.
http://members.aol.com/profchm/bpelevat.html
http://whatscookingamerica.net/boilpoint.htm
You can also just type it into google yourself.
It sounds like you might need to check your starting conditions for your experiment. Unless all of your water samples started at the same temperature, one might boil in less time than another but still be at a higher final temperature. You also need to make sure that you use exactly the same pot on exactly the same burner with exactly the same amount of water under exactly the same conditions to be able to compare two different types of water. It sounds like you measured the amount of time it took to boil the water. It might be more accurate to use a thermometer to measure the temperature of the boiling water in each case to see if there was any difference.