Do not try this at home! In order for this to occur, the water must be heated in a cup and cannot contain any impurities or additives. What happens is that the water becomes superheated - it reaches a temperature beyond its normal boiling pot (212�F). However, its container does not get very hot, so no bubbles are formed! If the water remains undisturbed and microwaves for long enough, the entire cupful could become superheated! Once it is removed from the microwave, all it needs is some sort of 'trigger' to let bubbles form and allow boiling to begin. Oftentimes, this trigger can be the addition of sugar, coffee, or a teabag.Don't worry though! This is highly uncommon - the conditions must be PERFECT for water to explode. If you are still not convinced, you can place a non-metal object in the water or add your tea, coffee, or sugar first. This will prevent the water from becoming superheated.