The legend is as follows:
Indra, the King of the Devas, was once driven out of Devaloka by an asura named Vritra. This asura was the recipient of a boon which made him invulnerable to any known weapon. This Demon, Vritra, also stole all the water in the world for his own use and for that of his Demon army. He did this so that all other living beings would die of thirst and hunger, leaving no Human or God alive to challenge his place in Heaven. Indra, who had lost all hope of recovering his kingdom, went to seek the aid of Vishnu. Vishnu revealed to Indra that only weapons made from the thunder-containing (called in Sanskrit as Vajra) diamond bones of the sage Dadhichi could kill Vritra. Indra and the other Devas therefore approached the sage, whom Indra had once beheaded, and asked him for his aid in defeating Vritra. Dadhichi acceded to the Devas' request, but said that he wished that he had time to go on a pilgrimage to all the holy rivers before he gave up his life for them. Indra then brought all the water of the holy rivers together at Naimisharanya, thereby allowing the sage to have his wish fulfilled without a further loss of time. Dadhichi then went into a deep meditative state and released his life force from his body. The celestial Kamadhenu Calf then licked and removed the flesh from his bones, after which the Devas fashioned the Vajrayudha (Thunderbolt) from his spine and made numerous other weapons. This weapon was then used to kill the asura, allowing Indra to reclaim his place as the king of devaloka and releasing the water for all living beings.
I am little confused here, my question is if Vritra stole all the water in the world then from where did Indra bring water? The statement seems a bit contradictory to me or maybe am not getting it right.