In Exodus 32:20, Moses breaks up the golden calf and pulverizes it into dust. Next he mixes it with water and has Israel drink it. This passage is clearly analogous to Number 5:12-31 where dust is mixed with water and then drunk in order to discover miraculously the guilt of a suspected adulterous wife.
Here is my conjecture and I'm looking for some helpful (or critical) comments. Could it be that the potion made by Moses serves as a "judging potion" that reveals who in the camp is guilty of idolatry. The Levites seem to know who to kill and who not to kill. The guilty are marked out somehow. From the literary structure, it seems that the drinking of dust water leads to the execution of the guilty.
In any event, the idolatrous act of calf-worship is an act of adultery against God. The spouse of God committed adultery against God through idolatry, she is tested with a dust potion and found guilty. The executioners are the Levites who then become priests.