In the Player’s Handbook the section for holy water states (emphasis mine):
As an action, you can splash the contents of this flask onto a creature within 5 feet of you or throw it up to 20 feet, shattering it on impact. In either case, make a ranged attack against a target creature, treating the holy water as an improvised weapon. If the target is a fiend or undead, it takes 2d6 radiant damage.
In both Curse of Strahd and Storm King’s Thunder characters can find vials of holy water, not flasks. These could be used as a material component for certain spells, but can they be used a weapon like a flask of holy water? If so, how would the damage differ?
The Player’s Handbook also defines the capacity of a vial as “4 ounces liquid” and a flask (or tankard) as “1 pint liquid”. So could a character combine four vials to use as a weapon?