It is possible to get hold of a test tube in which water is boiling. For this, the test tube is heated at the top side and not at the bottom. The heated water is lighter and stays at the top while there still is colder water at the bottom of test tube. 

That’s why we can hold the test tube comfortably.

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This answer points out a concept that hot water rises up. This is just like the case of air in which hot air gets up and cools down. But the question arises that why do the water or air rise above when heated? Why not go down! We get these answers from Science.

Every molecule is made from atoms, whether it is fluid or gas or solid. These molecules or atoms are always in motion (oscillatory motion) i.e. they have kinetic energy. When heated, the internal energy of these molecules increases and they start to oscillate with larger amplitudes. 

This causes these materials to expand as Expansion essentially means, low density –> low density means relative lightness –>motion towards topside (heavy gas or fluid move downwards due to gravity.)