Where did the excess water remaining from washing the Messenger of Allah, may Allah bless him and grant him peace, go?

There is no authentic narration proving that the Companions deliberately performed a specific act with the water from the Prophet's ablution after his death. Had there been a Sunnah or a prescribed law in it, it would have been transmitted. As for what is narrated about Ali seeking blessings from the water of the Prophet's ablution, it was narrated by Imam Ahmad with a weak chain of transmission. Even if it were authentic, it would only indicate the permissibility of seeking blessings from the relics of the Prophet (peace be upon him) and nothing else. Seeking blessings from other than the Prophet is a reprehensible innovation.