I infer you’re talking about an electric water heater. How old is it? Have you ever changed the sacrificial anode? If not, and it’s more than six years old, odds are that what happened is that it reached the end of its life and rusted out. Brown water coming out of an element port is not a good sign. If it’s younger than that, and you know how to use a multimeter, there is a general troubleshooting walkthrough under Electric Water Heater Issues in Tanklets, for which there is a link on the left side of the Tank topics index.
If the tank is a goner, consider reading the whole Water Heater Basics section of waterheaterrescue.com so you can make an informed choice and also have some idea of how to prevent this happening again.