One story could be about how some birds like hummingbirds drink nectar which is like a sweet 'drink' for them. They have long beaks to reach into flowers and get the nectar. Another could be about how camels can go long periods without water and then when they do drink, it's a large amount to sustain them in their arid environments. And some monkeys in the rainforest might drink water from tree hollows or from the leaves that collect rainwater.
Sure. Polar bears are a great example. They often get their water from the blood and fat of the seals they hunt. Since they live in a very cold environment where freshwater sources can be scarce, they've adapted in this way. So it's a rather unique way of getting both food and 'drink'.
A good approach would be to educate her about the body in a general sense. Start with basic body parts and functions. Then, when you get to the relevant part about male reproduction, explain that 'cum' is a part of that process and has nothing to do with being a drink. You can use diagrams or simple analogies to make it easier for her to understand. Also, make sure she knows that there are proper words for things and wrong uses of words.
No way. In most cultures and societies, there are clear boundaries in the relationship between parents and children. Sex - related topics are very private and should be taught at the appropriate time and in the appropriate way by professionals or in a more appropriate context, not by a mother to her son in the form of'sex stories'.