מקואות ב׳:ג׳ - ב׳:ד׳

ספק מים שאובים שטיהרו חכמים – In Tractate Tohorot, Chapter “He Who Threw Something Unclean [from Place to Place – chapter 4, Mishnah 7] there it teaches: “These are the doubtful conditions which the Sages declared clean: A doubt concerning drawn water [that falls into] the ritual bath.”

ספק נפלו – three LOG (i.e., a LOG equals the volume of six eggs) of drawn water in a Mikveh missing [its full complement of forty Seah]/

ספק יש בהן ארבעים סאה – that is to say, there is doubt that it were forty Kosher Seah [of water] in the Mikveh/ritual bath prior to the drawn [waters] that fell in, for furthermore, the drawn [waters] do not invalidate it (i.e., since it is lacking the required forty Seah to begin with).

שיש לו במה יתלה – that it has a place to depend upon their falling that they did not cause it to become invalidated.

שאין לו במה יתלה – that whichever way you turn, in which of them that it fell, it invalidates it, therefore, both of them are invalid. But that which we purify here – it is doubtful if is drawn water in the place where he has upon which to depend, that is because the [notion of] drawn [water] is from the Rabbbis. And it is taught in a Baraita in Torat Kohanim (i.e., the Halakhic Midrash of SIfra on the Book of Leviticus: - see Leviticus 11:36): “However, a spring or cistern [in which water is collected shall be pure, but whoever touches a such a carcass in it shall be impure],” that just as a spring is in the hands of Heaven, so also is a ritual bath/Mikveh in the hands of heaven, it is a mere support but not an absolute proof.

בתחילה – [at first], there wasn’t any water in the Mikveh/ritual bath at all when a quarter [of a LOG] of drawn water fell into it, and afterwards, its measure was completed with rain water.

על פני המים – after that there was a great deal of kosher water [in the Mikveh, drawn water fell into it].

וחכמים אומרים – and the Halakha is according to the Sages (and see Tractate Eduyot, Chapter 1, Mishnah 3).