I entered Vault 15 and descended to the command center, but no matter where i go i cant get the message that the water chip is nowhere to be found, i walk around the collapsed doorway but still dont get the message.

Hmm, never heard of this bug - just walking close enough to the rubble should've been enough to trigger the message... Not that you actually need to visit Vault 15 to progress in the main quest, mind you. So I guess you could try an earlier save to see if you get it to trigger, or just move on.

Yeah, when you walk near the computer rubble in the Overseer's area, it should tell you.

But you don't need to do V15 to progress the story.