Freshwater is the item that is the focus of the VacPack upgrade, Water Tank.
Sources
Once you find a source of water, hold the assigned 'Vac' key or button, and, assuming you have the Water Tank upgrade, the Water Tank slot should start filling up with water. There are several ways to get fresh water, constructing the Pond on a plot of land (which automatically fills), or finding it in the Far, Far Range, through Geysers and naturally occurring fresh water pockets, in which Puddle slimes naturally spawn in. Puddle slimes require water to survive. Puddle Plorts evaporate if touching something that is not water. The Tarr absolutely can't stand freshwater and spraying them with it dissolves the angry creatures.
Occurance
The naturally occurring Fresh Water springs and ponds exist in multiple Zones throughout the Far, Far Range. Notably being the one(s) in The Dry Reef Island, The Indigo Quarry, The Moss Blanket, The Docks, and other lands.
Note
- This is not referring to the vast and player and slime lethal Slime Sea.
- Related: Hydro Turret