I'd start with their own houses. Where do they thin the water does when it goes down the drain? Many municipal water systems have inforgraphics on their website showing the local water system. As you work through that, you could bring in the traditional water cycle....e.g., so the water sits in the reservoir. I wonder if it's muggy there. I know when I am the lake, it's often muggy. Lead them to think it through. If you live in an area where you have rain, it is much easier to do!