With the buckets being kind of deep, how do your ducks actually get water from there at all?
Well i wouldn't recommend buckets for really young(ie; small) ducks but most people aren't using heated buckets with ducklings. For smaller ducks in general (calls for instance) i'd probably recommend heated bowls vs buckets.
Anyways, i have 4 littler ones(6.5mths & 4.5mths) and they reach the 2Gal just fine.