I do know this and I sometimes take advantage of it. However, I feel a little awkward asking for 2 free waters as much as I drink. Plus, they don't taste that great. I know Disney makes money on water and I'm OK with that.
I know exactly what you mean, almost feels cheap and cheeky asking. Perhaps we're so conditioned to paying for anything and everything in the parks that we come out of our 'comfort zone' when asking for anything 'free'. It almost feels like begging for charity at first, but after the second time I did it I learnt to live with it and do it now without a care in the world
I can't bring myself to ask for free water if I'm not buying something as well. If I'm purchasing a meal, then I'm comfortable asking for an ice water with it since I don't drink soda. The rest of the time I just buy a bottle as needed. I also get 4 cases of bottled waters with my Garden Grocer order.