Many distilleries brag about their pure water supply, but typically that water is only used for fermentation, and then reverse osmosis filtered or distilled tap water is used to dilute spirits down to bottle proof. So the quantity of that special water left in the bottle is small - in the case of vodka it's just a few percent.
Some producers claim to use special water but then do the RO or distillation to it to remove minerals and other organic matter from it for bottling, making the special water a lot less special.
That's what I suspected was going on when I noticed that on the new Lucky Thirteen bottling from Widow Jane bourbon the label says, "Pure limestone water from the legendary Rosendale mines of NY."
So I asked their PR team for clarification- it would be pretty unusual to be using untreated/filtered water.
I heard back from Lisa Wicker, President and Head Distiller for Widow Jane. She wrote:
It is very unusual to use mineral-rich water for proofing! When I “inherited” proofing using water from the Rosendale limestone mines, it took me a while to determine how to handle it. We worked with water engineers on a withdrawal system that does not strip the minerals. The water tests beautifully, it does not need to be treated. Our cave is under lock and key for purity and we hold the only permit of its' kind in New York for withdrawing cave water as an ingredient. Finally, we “polish” the whiskey without chill and conventional filtration, which would have stripped the minerality out that makes Widow Jane whiskey, “Widow Jane.”
So, it turns out that they do something that I think is pretty unique. I will have to see if I can detect any mineralogy when I taste it.