Leviticus 14:5 - Clarke's commentary and critical notes on the Bible

And the priest shall command that one of the birds be killed in an earthen vessel over running water: Over running water - Literally, living, that is, spring water. The meaning appears to be this: Some water (about a quarter of a log, an eggshell and a half full, according to the rabbins) was taken from a spring, and put into a clean earthen vessel, and they killed the bird over this water, that the blood might drop into it; and in this blood and water mixed, they dipped the instrument before described, and sprinkled it seven times upon the person who was to be cleansed. The living or spring water was chosen because it was purer than what was taken from pits or wells, the latter being often in a putrid or corrupt state; for in a ceremony of purifying or cleansing, every thing must be as pure and perfect as possible.