Translation:We are thirsty, but we do not have water.
Almost correct! In both sentencens, 'hebben' should be at the end (because of the words 'waarom' and 'omdat').
'Dat is waarom jullie dorst hebben. Het is omdat jullie geen water hebben.'
Just out of interest: in Dutch is it obligatory to write a comma between the clauses in sentences like this? (It wouldn't be in English.)