Answers:
If you are in a marathon, you need to be hydrated in order to have energy to keep running. Therefore, you need to ingest water (agua), not a steak (bistec), a soda (gaseosa), nor a smoothie (batido).
If the question is:
¿De donde eres? (Where are you from?)
You must answer with the same verbal tense (verb TO BE in present) and the correct subject pronoun. In this case is yo (I):
I am from the United States
(Yo) Soy de los Estados Unidos
Note in Spanish grammar is not always necessary that the subject is explicitly in the sentence, it is called Tacit Subject, Implicit Subject or Null Subject.
This is because the subject is encoded in the verb conjugation
This is the right way to translate the sentence above, taking into account it is in present tense with the verb TO BE applied to the 3rd person in singular.
In Spanish (castillian) the verb TO BE means ser or estar. In this sentence we are talking about the composition (ingredients) of a food, in other words, what is the food made of.