Mikvaos 3:3-4

Mikvaos 3:3

If a cistern is full of drawn water and a channel leads in and out of it, it remains invalid until it can be calculated that three log of the drawn water no longer remain. If two men each pour a log and a half of drawn water into a mikvah, or if someone wrings his clothes into the mikvah thereby adding water from several places, or if someone pours from a vessel with a rose (multiple holes, like a shower head) into the mikvah thereby adding water from several places, Rabbi Akiva declares the mikvah to be valid, while the Sages rule it invalid. Rabbi Akiva pointed out that the early authorities didn’t say “if they poured” (requiring multiple people), but rather “if one poured” (i.e., even a single person). The Sages responded that they didn’t say either of these things. Rather, they said “if three log fell.”

Mikvaos 3:4

If three log of drawn water fell in from a single vessel, or from two vessels or from three, they combine; from four vessels, they do not combine. If a man who had a seminal discharge was ill (so that he couldn’t immerse) and nine kav of water fell on him, or if three log of drawn water fell on the head and the greater part of a clean person, from one, two or three vessels, they combine but from four, they do not combine. The part about two or three vessels combining applies when the second started before the first was finished. The part about four not combining applies when there was no intention to add more water to the mikvah; if there was an intention to add more – even if it’s only a kortov (1/64 of a log) for a whole year – they combine together to form three log.