another translation is: the water in the glass boils
More like "A cup of boiling water"
that's right , i agree with that... water in a cup can't boil
the water in the glass/cup boils
Seems like the conjugations of "bollire" are missing from Duo's definitions so here they are: (to boil) = bollire: io bollo, tu bolli, lui/lei bolle, noi bolliamo, voi bollite, loro bollono.
Although I'm sure "bolle" will be the most common word.