"Do you drink water?"
this can also be 'Unakunywa maji?' if you're addressing one person, since it's not specified whether it's singular or plural 'you'.
In most cases 'you are' and 'are you' are exactly the same, the difference being in punctuation. Although not necessary, sometimes 'Je' is added to show it is an inquiry ('Je, unakunywa maji?')
The breakdown: 'M-na-kunywa'
'M-' indicates the subject ('you' plural)
'-na-' indicates present tense
'-kunywa' is the verb stem (to drink)