Water Rune Pieces are by many considered to be the most useful of all rune pieces during the Gate Rune Wars, due to their ability to gradually restore HP to the character whose weapon is imbued with water. Compared to the relatively small bonuses of other rune pieces this is a very useful effect. Furthermore, in Suikoden I they provide the only possibility to damage enemies with the water element.
Water Rune Pieces are derived from the blue Killer Slimes that roam Mt. Tigerwolf and therefore can be obtained indefinitely at the beginning and the end of the adventure. In times of the Island Liberation Wars Water Rune Pieces were occasionaly traded among pirates, however at that time they didn't possess their curative powers already. - Celes