Dirty water

 is the most common water in the game, and is drawn from the tainted lakes and rivers of Fallout 3. Unlike Purified Water, this will give you radiation, which can be cured for a fee by your local friendly doctor, by using Rad Away, or by using your infirmary.

Dirty water differs in appearance from purified water. Dirty water is labeled "WATER", while purified water is labeled "H²O"; the bottle is also grimier. The Pip-Boy icon for both is the same, however.

Also note that you cannot purify this into purified water.