Two containers that have the same volume (let say 500 liter) but are different in shape

I remember from school, one time a teacher explain us the following:
two containers of the same volume, but one is thin and tall, and the second is short and wide.
then if we fill them with water from the same input, the container that is thin and tall will get filled faster.
he gave us some mathematical proofs on it, but it was 30 years ago.
does anyone knows if this is true and how can be proved?