Even when an item is given away for free at a public venue, it could potentially pose a risk to the public health. I doubt you can do coffee or tea, but it might not be too hard to acquire the permit to make those and offer them. For water, I really have no idea, but I’d like to think that that would be fine, assuming it is city water. Obviously, you would have no problem giving away commercially-bottled and canned drinks, but that can get pricey. You should talk with the ag dept about this, and if they don’t know, contact the health dept.