You can do the roll and let the GM decide. He gave you permission. Who knows? Maybe a well pump, an old pipe, a collection barrel, even a supply of Dwarven beer long forgotten!BillTheGalacticHero wrote:I doubt if there is any potable water in the tower, unless there's a rain collection barrel.
The main point is, his instinct is to check. Checking gives you a Survivalist test. Tests increase your skill over time. Make the tests.
If you're concerned about the water thing, I strongly suggest considering changing your instinct. "Always make camp safe" would be very valuable and more clearly of use. It is a different Survivalist test, has a clear trigger (making camp) and will likely save our lives from disaster.