Why does water put out fires?

The fire triangle is fuel (something that will burn), oxygen and heat. If you take away any of the three the fire will go out. Water reduces the temperature and causes the fire to die out. A note here: Water is used on class "A" fires only. A class "A" fire is anything that will leave an ash when burned such as paper, wood or cloth. If you were to try to use water on a class "B" fire (a liquid fuel fire) the water will cause the liquid to spread out rather than cool it and make the fire worse. A class"C" fire is anything electrical and while water may put the fire out you run the risk of electrocution if you use water. There is also a class "D" type of fire that includes metals such as magnesium that will burn. If you put water on burning magnesium such as an airplane wheel the magnesium may explode.