Hi, Andres! It is almost correct, the sentence should be: Yo bebo mucha agua en el gimnasio antes de mi rutina de ejercicio. As you see: "mucho" is replaced by "mucha", because of the grammar gender; "routina" instead of "rutina" and "de ejercicio" in place of just "ejercicio", in this case you should add the preposition "de".
Keep going! Greetings.