Adam Clarke on Numbers 5:24

The bitter water that causeth the curse - Though the rabbins think that the priest put some bitter substance in the water, yet as nothing of the kind is intimated by Moses, we may consider the word as used here metaphorically for affliction, death, etc. These waters were afflicting and deadly to her who drank them, being guilty. In this sense afflictions are said to be bitter, Isa 38:17; so also is death, 1Sam 15:32 : Ecc 7:26.