Translation:We do not have food, but at least we have water.
So can we also use "zumindest" in this context? "Wir haben kein Essen, aber zumindest haben wir Wasser." Or is there some subtle difference that I will find in https://yourdailygerman.com/2014/06/17/wenigstens-mindestens-zumindest-zumindest-difference/ ? (I have not got enough time to read the whole thing right now.)
Usage rule suggests that however is closer to in spite of than but; however, many English speakers use however and but interchangeably anyway.
My immediate reaction to the example was but and when I read your question I found however a bit odd especially with the inclusion at least.
why not: we have no food?
Because you did not translate the second part of the sentence ..., aber wenigstens haben wir Wasser.
Please always quote your entire answer, not just individual words. Often, if a sentence is not accepted, it's because of a problem somewhere else than you assume. Also, please copy and paste your answer into your comment; do not re-type it (which may introduce new typos or cause typos you made in the answer to Duo's question to disappear).