your balanced equation for this reaction is:
HCOOH (aq) + H2O (aq) → HCOO- (aq) + H3O+ (aq)
So from the reaction, we can see when formic acid dissolved in water so H3O+ ions will be formed.
and we can see that it is a balanced equation as:
we have H atoms = 4 on both sides of the reaction
and C atoms = 1 atom on both sides of the reaction
and O atoms = 3 atoms on both sides of the reaction
So it is our final balanced equation of the reaction.