Photo courtesy FEMA
If you own a house, you own a water heater. You probably don't spend much time thinking about the water heater until, one morning, you go to take a shower and there's no hot water. Then you probably think about it a lot.

And if you're the curious sort, the following water-heater question may have crossed your mind: "How can the water stay hot if cold water comes in as soon as you start using the hot water?"

In this edition of HowStuffWorks, we will take a look inside a typical water heater so you can understand how it works -- and why it sometimes doesn't.