I have finished my first full year of travel last year and from my observations, its been very random these days at hilton group.
Some locations do give two bottles of water (For eg. Hilton Orange County), some do give just one bottle of water and some don't give any thing. In some locations, if you are a diamond member, just walk over to the executive lounge and most of the time, you would find bottles of water in the refrigerator. I usually pick up a couple once in a while from the exec lounge. And some locations don't have them in the exec lounge as well in which case, you are left on your own to buy them.