Water rune

The water rune is one of the four elemental runes, consisting of Air, Earth, Fire. The are used for the most basic and advanced water and ice spells. If you have one water rune in your inventory and are weilding a Tome of Frost you have the ability to have unlimited water runes. Alternatively if you are weilding a water staff you can also have an unlimited amount of water runes.

How to get
You can craft runes via Runecrafting with level 5 Runecrafting in the Water alter in Lumbridge and walking south to the swamps. You can also buy Water runes from other players, or from Zaff.