Mikvaot, Chapter Three, Mishnah Three
1) If a cistern is full of drawn water and a channel leads into it and out of it, it continues to be invalid until it can be reckoned that there does not remain in it three logs of the former [water].
2) If two men each poured a log and a half [of drawn water] into a mikveh, or if one wrung out his clothes and so poured in [water] from several places, or if one emptied out a water-jug and so poured in [water]from several places,
a) Rabbi Akiva declares it valid,
b) But the sages declare it invalid.
i) Rabbi Akiva said: they did not say “if they poured in,” rather “if one poured in.”
ii) But they said: they said neither thus nor thus, but rather “if there fell in three logs [of drawn water].”
Section one: The water flowing through the channel is valid to be used as a mikveh. It will validate the cistern full of drawn water when we can assume that the channel has flushed out most of the drawn water, leaving no more than three logs worth in the cistern.
Section two: Rabbi Akiva says that for three logs of drawn water to invalidate a mikveh, they must all come from one source made in one pouring. Separate pourings do not join together to invalidate the mikveh. The water-jug to which he refers seems to have multiple spouts, so if one person pours in, it gets there in several pouring.
The other sages disagree. Three logs of drawn water invalidate the mikveh even if they come from multiple sources.
Both Rabbi Akiva and the sages derive their halakhah from a precise understanding of their received oral tradition. Rabbi Akiva’s mishnah reads “If one poured into a mikveh three logs of drawn water he invalidates it.” Rabbi Akiva reads this mishnah preciselyit is invalid only if one poured three logs in. If two or more together poured three logs into the mikveh, it is not invalid.
The other sages have a different reading in their older mishnah. There mishnah reads “if there fell in ” There is no difference how these three logs got in. Their very presence invalidates the mikveh.
As an aside, this is one of the most interesting examples I have come across of two sages arguing over the wording of an ancient mishnah. It is a clear example of the fact that prior to the generation of Rabbi Akiva there already existed an oral Torah upon which each sage could base his argument.