The Sotah-ritual in Num 5:11–31 has been the focus of many interpretations, part of which is how we understand what the potion used in the ritual is supposed to do. Among these Roy E. Gane has argued that it is the dynamic of holiness versus impurity that creates the effect of the potion (2016), and Yitzhaq Feder that the waters so to speak seek out the impurity of another man’s seed in the woman and punish her (2022). But what is the rationale behind this? While it is impossible to know the details, the line of argument followed in this paper is to say that the genitive mey ha’arim (water of bitterness, v. 18, 19, 23) should be understood objectively as indicating what the ritual is about, and not indicating the harmful effect of the potion. At the same time, the text describes that upon taking the potion the woman’s womb discharge and her uterus will drop (v. 22). So how does this come about if the potion in itself is not harmful?  The argument made here is that this is because the potion is considered holy, in that holy water is used for it (v. 17), while the woman is considered (potentially) impure (v. 27), and that it is this meeting of holy and impure that creates the harmful effect. This understanding is strengthened by the use of dust in the ritual (v. 17). It is not described as holy, but it is taken from the floor of the (holy) tabernacle. Furthermore, rituals in Zoroastrian religion during Persian times, roughly contemporary with the composition of the book of Numbers, use dust for purification, thus forming suggestive parallels to interpret the Sotah.