There is a physical property called "specific heat". This property determines the amount of temperature necessary to change 1ºC in the temperature of the materials. The higher the specific heat of the material, the slower it will heat up.
The water has an extremely high specific heat, which means that it will slowly heat up to an extremely high temperature. The specific heat of the water is greater than most materials and this explains why high variations and external temperature changes almost do not cause changes in the water of the picisnas, for example.
