Numbers 5:17
“And the priest shall take holy water in an earthen vessel; and of the dust that is in the floor of the tabernacle the priest shall take, and put it into the water:”
When a man thought that his wife committed adultery with another man, he was to go to the priest to settle the problem. The priest would then take an earthen vessel and put holy water in it, that is water that was separated from being used for any other purpose other than for the temple, and he would make the woman who was accused of adultery drink the water. If she were guilty, the water in the vessel would cause her thigh to rot and her belly to swell.