Mikvaot, Chapter Three, Mishnah Two
Today’s mishnah is a continuation of yesterday’s. It explains how a mikveh that has been disqualified because three logs fell into it can again become valid.
1) 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.
2) Rabbi Elazer ben Azariah declares it invalid unless the [new mikveh] is stopped up.
Section one: The mishnah provides two ways to revalidate a mikveh that has been declared invalid because of three logs of drawn water. The first is to remove all of the water and then allow new valid water to flow in. This is the solution we saw in yesterday’s mishnah.
The second way of validating the mikveh can work if there are two cisterns in the courtyard, one higher than the other. The higher one is the one that has been made invalid. He can add water to this cistern so that it overflows and the water will flow down into the lower cistern which also has less than forty seahs of water. The water flowing from the upper cistern will cause the lower one to have more than forty seahs and it will be pure. By virtue of its connection with the lower cistern which is valid, the higher cistern is also validated as a mikveh. We shall learn of this principle below in 6:8.
Section two: Rabbi Elazar ben Azariah says he must stop up the upper mikveh, and then the bottom mikveh will fill up with forty seahs of valid water that he has allowed to flow into the courtyard and then he can attach the two mikvaot. But if he doesn’t stop up the upper mikveh, then the invalid water will flow into the lower mikveh and it too will be invalid.