Water-Runes are runes you need for certain Magic spells. It's one of the 4 elemental runes. You can buy them from Aubury in Varrock, Betty in Port Sarim, or at the Wizards' Guild. Wielding a Staff of Water means that you do not need any water-runes in your inventory to cast spells. These items have a street price of around 30-50 coins each. They are used in the following spells: