Rule reminder
Backshift is OBLIGATORY when the reported event belongs to a completed past. Backshift is OPTIONAL (both tenses correct) when: 1) the reported fact is still true at the time of reporting, 2) the statement is a universal truth, 3) the reporting context is clearly 'simultaneous' present. This nuance is crucial at B2 level.
Yesterday Anna said: 'L'acqua bolle a 100 gradi.' Today you report this. Which is correct?