The Ultra Divine Water (超神水, lit. Super God/Divine Water) is a magic water that will draw out all of the drinker's potential if they can survive its poisonous and painful effects. Thus, if a drinker has already obtained their full potential it will have no effect.
In the Dragon Ball anime, according to Darkness, thirteen people drank the water before Goku and they did not survive. After Goku's defeat by King Piccolo, the former turns to Korin for a way to avenge the loss of his friends. In the Dragon Ball manga, the water is in Korin's possession and he gives it to Goku almost immediately after telling him about it. In the Dragon Ball anime, using one of his magic pots, Korin transports Goku to an icy maze to the north where the Ultra Divine Water is kept. Moments prior to Goku's being sent through, Yajirobe was looking for food when he inadvertently fell into the same pot that would send Goku to the maze. After navigating to the Cave of Darkness together, Yajirobe and Goku parted ways. Goku soon encountered an illusion (created by Darkness) of Master Roshi, and all of his friends, who claimed to be hiding there from King Piccolo. He fought "Master Roshi", and was almost defeated before his persistence convinced Darkness that Goku was worthy to drink the Ultra Divine Water (during the battle, Goku was reunited with Yajirobe again).
Yajirobe dipped his finger into the Ultra Divine Water and tested it before Goku drank it, as he thought it was poison. It caused him painful effects for a few seconds, which led him to urge Goku not to drink the Ultra Divine Water (as Yajirobe did not die after sampling the water, it can be assumed that either the Ultra Divine Water must be drunk in larger quantities to either kill or improve the strength of the person, or that only a little bit was enough to increase Yajirobe's strength a tiny amount, but not nearly as much as Goku's). Upon drinking the water, Goku writhed in agony for some time and his life flashed before his eyes. After he had endured the pain, his increase in power was great enough that Korin was able to detect it from his tower. This newfound strength was crucial to Goku's defeat of King Piccolo shortly thereafter. Via the Ultra Divine Water, Goku also learned the Ki sensing ability; he remarked about this newfound ability to Korin when he stated that he knew where King Piccolo was.
According to Darkness the liquid is sacred and not meant for humans. Later he states thirteen people had drank the water and none survived, making Goku the fourteenth and the only known survivor up to that point. Since Goku is the only stated survivor and a Saiyan, it is unknown if any human could actually survive its trial. It is possible that his Saiyan heritage actually played a large role in his survival, which could explain the Great Ape appearing just after Goku's power increases and just before he kills King Piccolo.
Video game appearances
The Ultra Divine Water appears in Famicom Jump: Hero Retsuden and Dragon Ball 3: Gokuden. It is a treasure item called Mystic Water in Dragon Ball: Advanced Adventure; if the player finds it, they will be able to use it.
In Dragon Ball Z: Budokai Tenkaichi 3, drinking the Ultra Divine Water in the Sim Dragon mode levels your character up and gives him a huge increase in strength (just as it normally would). In Dragon Ball: Raging Blast 2, Ultra Divine Water is an equipable item that causes the equipped character to go in a Hi-Tension state when he is at one bar of health. In Dragon Ball Z: Tenkaichi Tag Team, Ultra Divine Water is an Ability type D-Item that increases by 20,000 the maximum health; it requires 3 columns in Ability type. In Dragon Ball Z: Battle of Z, Ultra Divine Water is an item that increases all abilities for one minute.
- It is believed by some that Kami is somehow connected with the Ultra Divine Water due to his symbol actually appearing on the pot containing the water before Kami himself appears. However, it is likely all guardians wear the symbol (as evident by the fact his successor Dende was also sometimes portrayed wearing it), as Kami means God in Japanese.
- It can be assumed that the Ultra-Divine-Water had a greater effect on Goku than say, a human drinker, because of the quirk in his Saiyan Physiology: an exponential increase in power if one recovers from the edge-of-death. So whereas the water would only make a human stronger, a Saiyan would be made doubly powerful by cheating death caused by its toxic venom.