In the book of Numbers, a ritual involves drinking “bitter water” to test a wife’s faithfulness to her husband. This ritual was performed if a husband suspected his wife of committing adultery or had feelings of jealousy, putting her faithfulness into question (cf. Numbers 5:29-30). You can read about this here (Numbers 5:11-31).

This ritual involved drinking holy water mixed with dirt from the temple floor. In addition, whatever ink was used in writing scrolls would be mixed in with the water since there would be “curses” written on the scroll that would fall upon the woman if she were guilty of adultery. 

There’s one verse people use to advocate abortion in Numbers 5:11-31. 

Here the priest is to put the woman under this curse—”may the Lord cause you to become a curse among your people when he makes your womb miscarry and your abdomen swell (emphasis added).

Numbers 5:21 (NIV)

The NIV’s use of the word “miscarry” is unfortunate because that’s not what the text says. While the text indicates something might happen regarding the womb, the best interpretations suggest there might be fertility issues. In fact, according to Jewish tradition, pregnant women weren’t allowed to participate in this ritual (Mishnah Sotah 4:3). Furthermore, there was nothing in the water that could cause any of the effects described. Thus, this ritual had nothing to do with terminating pregnancies. 

The ritual itself appears barbaric and chauvinistic. However, the alternatives to such a ritual were spousal abuse and murder. If a man suspected his wife of adultery, he might beat her or have her stoned to death as an adulteress. This isn’t a good situation either, but when women didn’t have any rights, the ritual of bitter water helped prove the innocence of women suspected of adultery and kept them from the harm that might otherwise have fallen upon them.