Learn Spanish (Latin America): Nosotros comemos pan y bebemos agua.

Both verbs end in -emos. In Spanish, regular verbs that end in -er (like comer and beber) drop the -er and add -emos to mean "we" do the action.

Do I always have to use nosotros before the verb?

No, it is usually optional! Because the -emos ending on comemos already means "we", you could just say Comemos pan y bebemos agua. Adding nosotros at the start just gives a little extra emphasis.

Why isn't there another nosotros before bebemos?

Just like in English, you do not need to repeat the subject for the second action. The -emos ending in bebemos makes it perfectly clear that "we" are still the ones doing the action.

Why isn't it el pan and el agua?

When you talk about eating or drinking an unspecified amount of something, you leave out the word for "the", just like in English. If you said comemos el pan, it would mean you are eating a specific loaf of bread ("we eat the bread").