Here in his editing for the 1837 edition, Joseph Smith changed the past-tense modal might to the present-tense may. The tendency in modern English is to interpret might in this kind of sentence as conditional in meaning. The original Book of Mormon text, on the other hand, often uses might without such a conditional sense. For discussion, see under Jacob 5:13. As explained there, the critical text will restore original uses of nonconditional might.
Summary: Restore the use of the historically past-tense modal might in Alma 17:26: “that they might have water”.