Kharidian cacti can be found around the Kharidian Desert. They can be used to fill waterskins by one dose. Similar to webs, a knife or a slash weapon is needed to cut them open.
Successfully cutting a cactus and filling a waterskin will display the text, "You top up your skin with water from the cactus" and award 10 Woodcutting experience. Failing to do so will display the text, "You fail to cut the cactus correctly and it gives no water this time" and award 1 Woodcutting experience. A dry cactus will become healthy again after 1 minute.