Rabbi Yose says: two mikvehs neither of which contains forty seahs and a log and a half [of drawn water] fell into this one and a log and a half into this one, and then they are mixed together, they remain valid, since they had never been called as invalid. But if there is a mikveh holding less than forty seahs, and three logs [of drawn water] fell into it, and it was then divided into two, it is invalid, since it had already been called invalid. Rabbi Joshua declares it valid, for Rabbi Joshua used to say: any mikveh containing less than forty seahs into which three logs [of drawn water] fell and from which a kortov was withdrawn becomes valid, since the three logs have also been diminished. But the sages say: it always remains invalid until the amount of its former contents and a little more are removed.

How so? If there was a cistern in a courtyard and three logs [of drawn water] fell into it, it will always remain invalid until the whole of it is removed and a little more, or until [another mikveh containing] forty se'ahs is placed in the courtyard, so that the higher mikveh is rendered valid by the lower. Rabbi Elazer ben Azariah declares it invalid unless the [new mikveh] is stopped up.

[If the three logs of drawn water fell in] from one vessel or from two or from three, they combine together; but if from four, they do not combine together. If a man who had a seminal issue was sick and nine kavs of water fell on him, or if there fell on the head and the greater part of the body of a clean person three logs of drawn water from one vessel or from two or from three, they combine together; but if from four, they do not combine together. In what case does this apply? When the second began before the first finished. And in what case does [the other statement] apply? When there was no intention to increase it. But if there was an intention to increase it, if only a kortov in a whole year, they combine together to add up to the three logs.