so I entered vault 15 and have been there for an hour. where is the water chip? I've been every where found all the loot and i still can't find this thing. I tried using explosives on roc walls but nothing happened. what do i do?

You won't find the water chip there (that would be too easy, wouldn't it). Go explore the world.

When going to the bottom level of the vault, you should receive a message in the status box stating that you won't find it there.
Kill the rats, use Science on computers, collect the loot and go back.
You should have the location of Junkyard on your map - that's your next stop.
If you don't, you need to talk with some of the people in Shady Sands.

(a) Junktown is a good next stop, but not necessarily the next place your character will think to go. Some luck and a little wits might even put you near the old Bakersfield ruins much earlier. Still, if the player's that stuck, I do agree that Junktown's the place to go.
(b) Just for the sake of asking, are you sure there are uses for Science on the computers in Vault 15? I've played the game a goodly many times and have never found those rooms useful for scientific purposes. Other uses, sure, but Science?

I agree.You don't have to use Science on the computer to check if the water chip is there.

I was wondering if he thought you could learn from the computer systems down there the way you can from the ones in Vault 13.

I might be wrong, but going science on them computers may yield a small xp gain.

From what i remember,ALL of the computers in V15 are off,except the one that should host the water chip.

As I recall it, all electronics are dead in V15 in Fallout 1. You might be mixing it up with Fallout 2....

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Heck, as I recollect, the Vault 15 water purification control computer isn't even accessible short of more explosives than your character could hope to encounter in the entirety of the Wastes.

That's how I remember it. It's possible I'm wrong - last time I played the game has been three years ago.

As I recall, you do get a response out of them, but not an electrical or useful one, just a message saying they're beyond assisting you.