Purified water is water that has been purged of any radiation, making it one of the only "clean" sources of water in the wasteland. The effects of purified water are modified by the Survival skill; the higher your skill, the more Hit Point and Dehydration it will restore. When playing hardcore mode, purified water is a more "refreshing" drink than alcohol or soda.
Effects of Survival skill
+2 Hit Point, -60 Dehydration
+4 Hit Point, -110 Dehydration
+2 Hit Point, -70 Dehydration
+4 Hit Point, -120 Dehydration
+3 Hit Point, -80 Dehydration
+5 Hit Point, -130 Dehydration
+3 Hit Point, -90 Dehydration
+5 Hit Point, -140 Dehydration
+4 Hit Point, -100 Dehydration
+6 Hit Point, -150 Dehydration
While there is no specific recipe for purified water, there are recipes for "cactus water" and "mass purified water", both of which produce purified water in different quantities from different components.
The Mojave Wasteland has multiple natural sources of pure, non-radioactive water, and as a result the player encounters clean water more often than in Fallout 3, where most of the water is radioactive.
Purified water can also be bought from several merchants, including the Kings member who guards the water pump in Freeside. The player can also fill empty bottles in The Sink with the Old World Blues add-on.
Prior to patch 126.96.36.1994, the recipe for mass purified water required 30 bottles of dirty water, 3 glass pitchers, a pressure cooker, a RadAway, and three surgical tubing, and produced 20 bottles of purified water.
Similarly, the recipe for cactus water required three prickly pear fruits.
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.