Necessities of Morrowind. I believe it's a mod that allows you to eat and drink to survive. It's quite popular.
I believe it actually
requires you to eat, drink, and rest in order to survive. It makes gameplay quite different, so be sure you back up your save, just in case you decide you want to take it out later.
Edit: Also, as I recall, there's some specific rules about where it goes in your load order, so also be certain to read the readme, else it might not work correctly.