In a random occurrence, you may encounter two groups fighting over a fridge stocked with 10 purified water bottles. You can leave them alone, kill them and take the water, or with a successful speech check, convince them to split the water with you.
There is also another random encounter which involves two wastelanders requesting you kill a radscorpion guarding a refrigerator with about 7 bottles of purified water. They will then allow you to take all the water.
Each bottle of purified water appears featuring the text "'H²O" hand written on the label on the side of the bottle. This format is incorrect (according to IUPAC nomenclature), as chemical formula numbers are written in subscript (Xy) and not in superscript (Xy). If read literally, the chemical formula H²O would mean there is one hydrogen and one oxygen isotope that contains two neutrons (instead of the standard eight). This would leave the oxygen extremely unstable and radioactive with a half life that would be so small that it would not be measurable.