Based upon my Park Stats, it is teenagers which are tipping this thirst issue, and since they have no money and probably have a stricter budget, their lack of ATM use may explain it. The only answer is to offer drinks at discounted prices.
However, our guests have no idea which drinks would be discounted, or where they are, until the stumble upon them. I personally discount one of the Soda drinks and make sure their are plenty synced around the park.
Does this help? Not greatly, because I have other drinks stalls, and I find spamming drinks stalls, especially discounted ones, is pointless if guests dont frequent every area of the park. This is probably why a mixture of food areas in highly populated areas, and the odd drinks stall in between, is a step in the right direction.
What would help is a precise ratio and we could just do the math: How many drinks stalls does it take to satisfy penniless Teenagers thirst?
And then we go back to the problem of having to discount prices because Teens are less with money, so we could find ourselves in the red.