There are "Rainbarrel only" versions and "Project Realism" versions that focus on melting snow for drinking water. General Concept: Melting Snow for Water
The phrase you are referring to typically points to a popular community-created mod for the survival game . Project Zomboid Mod: "Snow is Water" There are "Rainbarrel only" versions and "Project Realism"
The mod Snow is water [B41.74 Legacy] (or its variations) fixes a logical gap in the base game: by default, rain barrels do not collect water during winter when it snows. There are "Rainbarrel only" versions and "Project Realism"
It takes a large volume of snow to produce a small amount of liquid water (the ratio is roughly 10:1). There are "Rainbarrel only" versions and "Project Realism"