Water is often used to represent the flow of electrons in many college classes. Components are also given the water analogy. A resistor, for example, is a section of a pipe that constricts the flow of water, just like how it resists the flow of electrons. A capacitor is a balloon, though I don't think this is the best example.
Take a look at the Wikipedia page concerning the water analogy. I don't like the Wiki take on inductors.
Also, I once found a water analogy of an Op-Amp that explained how they work in a very clear way. I can't seem to find that one anymore. If anyone knows of one, please post the link.
I want to put together a thorough list of water analogies for all discrete components. It's a good reference. So, please post what you can.
Cabe