Water is a consumable item, available in all three Risen games. The effect of this item changes, however, from one game to another.
As most liquids in the game, water restores mana rather than health. Drinking this will add 5 mana to the character's total, never exceeding the maximum level of mana available to him. (Oddly, although carried water — i.e., in your inventory — restores mana, drinking from a water barrel restores health.)
Potion Ingredient Edit
Water is also used as an ingredient in brewing certain potions.
Risen 2 and 3Edit
Once added to the character's inventory, water is immediately converted to a provision. Once converted, it works as any provision (see that page for details).
Water in the later games is found as an item to be taken or looted, such as off a table. As shown in the image to the left, the item exists as water in these types of locations. It is only after adding it to a character's inventory that it is converted and no longer found under its previous name.