Yes, I thought fetch would be ok. Since when someone says "I have to get water", they usually mean they are going to obtain it and bring it back, which is closer to fetch.
I mean, contextually, yes, that has the same exact meaning, but for the sake of the lesson, they probably want you to use the verb "få" and its English translation, "get".
I answered "I must find water" which was marked incorrect. Is the true meaning of "få" "get" as in bring or fetch rather than find ?
Få means I have to get water somebody else, not by myself? Someone has to give that water to me, for example at a restaurant.