The Water Obelisk Island is a small island south of the Catherby fishing grounds. There, players can find the Water Obelisk and cast Charge Water Orb (with 56 Magic, sufficient runes and an uncharged orb).
To get to the island, a player must travel to the black dragons area in Taverley dungeon, and climb a ladder nearby. There is a one-way grapple shortcut from the island to Catherby which requires 36 Agility, 39 Ranged, and 22 Strength. A hidey-hole can also be built here.