That doesn't mean the same thing though. It's essentially a command telling you to drink water and what doing so would accomplish. The assumption is that the person telling you to drink water already knows that you are thirsty.
Telling somebody to drink water if they are thirsty does not tell them what it accomplishes. I could tell you to give me money if you are thirsty, but telling you to do something if you are thirsty doesn't tell you why doing that would help anything.
More to the point, this isn't about what you might say to somebody but about what the statement being translated means. It means that you should drink water to stop thirst.
It isn't remaining entirely true. I don't know if the original sentence being translated is used in modern German, but the English translation given is not used in regular English speech. That is all I was trying to say. Since this is a German course and not an English course, I translate it the way DL wants me too, even if it sounds strange/dated to a native English speaker.
It's an awkward sentence to translate because of the lack of articles and the inclusion of articles. I would say "drink THIS water to quench YOUR thirst", I would seldom say "drink (space) water for the thirst". It just sounds wrong. There need to be a few more words to make it specific to a context otherwise it just sounds weird.
Since Duo normally says the best tranlation for "Ich habe Durst" is "I am thirsty." The two translations below should be acceptable.
Drink water, if/when you are thirsty.
If/when you are thirsty, drink water.
But "Drink water to quench your thirst." I would say is the best formal Translation.
I feel that Duolingo may not accept "Drink water if you are thirsty" because, as stated earlier by Envacance, the goal of drinking the water (quenching your thirst) is not included. It is only implied, and therefore all information is not perfectly transferred.
Although I suppose not all information is transferred in a lot of translations anyway.
I think that "Drink water for the thirst" would be good English, given an appropriate context. For example, if I describe some symptoms including thirst to a doctor, I might be told "Drink water for the thirst".
If I understand you, you are saying that "Drink water for the thirst" does not mean the same as the German sentence. I defer to you on that point; I'm not confident in my interpretation of the German sentence.
However, "Drink water against the thirst" does not fit the context I proposed above, nor any other that I have yet thought of. It seems like bad English, rather than merely a mistranslation.
I am a native US English speaker and I try to always do two translations from German to English. The first is word for word "drink water against the thirst". This is the most important part, because i am not going to translate german to english for other people, only for me to understand the meaning. But also how i would want to say it if i'm trying to speak german. So, in common english conversation, we would not usually use the noun "thirst", there is no way to directly translate this sentence english and have it sound common. But you can usually translate things directly that are acceptable english, "Drink water to counter the thirst." is the translation i will use in my head.
Either is ok for 2nd person singular (du form). "Trinke" is less used, but my (German-speaking) husband says you might put an "e" on the end of a "du" imperative, depending on the sound of the following word, to make the sounds flow together better. He thinks using the "e" form might also be a bit regional.
Doesn't "gegen" mean thirst?
I assume you mis-wrote this, but I'm not quite sure how to interpret it.
Then shouldn't this phase mean "drink water against the thirst?"
Yes, the word-for-word translation is "against the thirst," but that sounds very strange in English. "Drink water to quench your thirst" sounds better and means about the same as the German sentence.
It's a matter of context. A nurse talking to a patient might say “Drink water when(ever) you're thirsty” = „Trink(e) Wasser wenn du durst hast.“, but in an informational brochure, the impersonal “Drink water when thirsty.” = ‘Trinke Wasser gegen den Durst.“ oder „Gegen Durst Wasser trinken.“ would be more likely.
I would think it only applies with "Durst" but I am only thinking from an English point of view not a German one! You may wish to look at the Oxford English dictionary of "quench" though - https://en.oxforddictionaries.com/definition/quench I don't know if you can use the german expression " gegen den Durst" for all of these "quench" uses - I suspect not. Perhaps a native German speaker can answer your question better than me.
"trink Wasser gegen den Durst" was not accepted as correct. I was told it should be "trinke". There have been several comments over 5 years on this thread asking why the e is needed but no explanations. The report button does not give the option of 'my answer should be accepted'. Come on Duo, this is supposed to be teaching us German. How can we learn if we do not understand our mistakes?
I would say the translation is still wrong as "Drink water to quench your thirst" because it says "your", which is not correct translation for the "den Durst". The ideal would be to change the German expression to "dein Durst", but as non German native, I'm not sure that would be possible.
It's very literal, not really fluent English, but people would understand it. I guess that's all they wanted. This time.
Edit By the way, please delete your 2 duplicate posts - they have moved down the page, due to people downvoting them. This page in particular has enough clutter! (And yes, I know that Duo lately has been taking so long to post a comment it's easy to suppose they didn't get it and post again.)
No, that's not a natural English sentence at all; I'm not even sure it would be understandable. You need something like "Drink water to quench your thirst."
In addition, you have "Drink the water" but the German sentence just has "Trinke Wasser." I'm rather surprised Duo accepted your translation, to be honest.
That's not an understandable English sentence at all. I'm not sure what you're translating as "goes" either; there's nothing in the German sentence that means that. (Perhaps you meant something like "Drink water. Your thirst goes [away]," but that's pretty different from the German sentence.)
I'm not sure I understand your question. Are you asking why you can't use "trink" instead of "trinke", or why you can't put it at the end after "Durst"?
To answer both of those, you can use "trink," and imperative sentences always put their verb first. If this doesn't answer your question, please rephrase.
"Trink" and "trinkt" are both also correct. Most "du"-form imperatives can be equivalently said with or without that "-e" ending. Both "trink" and "trinke" are correct for a "du" imperative, and "trinkt" is correct for an "ihr" imperative. Duo just happens to use "trinke" in this particular exercise.