This refers to things caused by the bad water. This also can be written in positive form. AT: "there will be no more death or problems with crops caused by this water" or "from now on this water will bring life and help the land become fruitful" (See: [[rc://en/ta/man/translate/figs-doublenegatives]])
This means that something remains in a certain condition until the present time. AT: "by the word which Elisha spoke, and have always remained pure since" (See: [[rc://en/ta/man/translate/figs-idiom]])