I found a great mapping website. I really like the diagram Yana found, where the catch basin branches out and resembles almost exactly the root system of a plant. Anyway, I just quickly did a topographical map showing the contour of the land in our region. It's not as detailed as I'd like but something worth looking at. In the site you can also select/deselect various icons and information to show. I highly recommend exploring the site, you have access to tons of information and there is even a section specifically on "Freshwater." From what I can see there's maps ranging from % of people harvesting ground water to where/how it is consumed.