The Waters of Truth was the name given to a liquid created by the Kouhun, a secret society named after a creature of the same name, for ritualistic purposes. It was brewed from many sources, including the venom of a kouhun, and kept in the Necropolis of Mataou. Those who wanted to join the society had to drink some of that liquid as part of their , although they would not learn of its high toxicity until after the rite was accomplished. Without treatment, the body of the drinker would start corrupting slowly. Over weeks, he or she would become severely impaired both physically and mentally. The Kouhun society, however, would administer a cure to those hopefuls who would survive the initiation tests with the poison coursing in their veins. The substance was also used by the Nightsisters.