If I understand correctly, "Du" is the 2nd person singular (you, as in just you alone), whereas "Ihr" is the 2nd person plural (you as in 'all of you' - I will use it if I'm refering to you and a specific group of people associated with you at the current time; "Ihr" might also be an honorific form to adress higher-ups such as teachers, elders and people higher by "rank", so to say, for example, your boss, - at least that's how it is in other languages, but I'm not sure of this particularly in German). It's common to separate them in many European languages, e.g. French - "tu" and "vous", I think Spanish has it, too.
Ich habe - I have Du hast - You have Er hat - He has Sie hat - She has Es hat - it has ( neuter) Wir haben - we have Ihr habt - You have Sie haben - They have
Ich bin - I am Du bist - You are Er ist - he is sie ist - she is es ist - it is ( neuter) wir sind = e are Ihr seid - You are Sie sind - They are
Now, German - like Russian and many other languages is AN INFLEXED language, this means that the ending of the words ( nouns, adjectives) change according to their gramatical position in the sentence.
I see that many of you, young men and women mostly, did not study grammar in your mother tongues. I strongly recommend you to do it now because if not, you will have big difficulties with German.
When 'have' is used with a past tense verb, it's called 'present perfect' ...so it would still be a 'type' of present tense. However "got" is in the past tense. Thus, if you were to replace 'got' with just "have", you would get the correct present translation.
Est-ce que ça fait sens?
"Harry, Ron, and Hermione: you have to go back to your rooms now!"
Some people use "ye" or "yinz" or "y'all" or "all y'all" or "you guys" or other forms for the plural "you", but this course just uses "you".
(It sometimes accepts "you all" and/or "you guys" but usually not any other forms.)
Article usage in German is broadly similar to that in English -- no article is needed before indefinite plural nouns in positive sentences or before indefinite uncountable nouns in positive sentences.
Here, Wasser is uncountable and indefinite, so no article is necessary.