Mikvaot, Chapter Seven, Mishnah One
1) Some materials raise the mikveh up [to the required quantity] and do not make it invalid.
2) Some make it invalid and do not raise it up [to the required quantity];
3) And some neither raise it up [to the required quantity] nor make it invalid.
4) These raise it up to the required quantity and do not make the mikveh invalid.
a) Snow, hail, frosted dew, ice, salt, and thin mud.
5) Rabbi Akiva said: Rabbi Ishmael once argued against me saying; snow does not raise up the mikveh [to its required quantity].
a) But the men of Madeba testified in his name that he had once told them: go and bring snow and with it prepare a mikveh from the outset.
6) Rabbi Yohanan ben Nuri says: hailstones are like drawn water.
7) How do they raise it up [to the required quantity] and not render it invalid?
a) If the mikveh contained forty seahs less one, and a se’ah of them fell in and made up [the required quantity], they thus make up [the required quantity] but do not render it invalid.
Sections 1-3: These sections serve as an introduction to the next few mishnayot which will explain each section and case, one at a time.
Section four: If one of the following materials falls into a mikveh that does not have forty seahs, and with the addition of the material the mikveh now has forty seahs, the mikveh is valid. In addition, if any of these materials fall into a mikveh, they do not invalidate it, even if they were put into a vessel. In other words, these materials can only benefit and not harm the mikveh.
Section five: Rabbi Akiva says that Rabbi Ishmael tried to argue that snow does not count in raising the mikveh up to its requisite amount. However, his argument failed because some men from Madeba (a city in Jordan, there is a famous mosaic map of the Holy Land there) testified that Rabbi Ishmael once told them to fill up a mikveh with snow, even though he wasn’t sure if this was valid.
We should note that this is a very interesting and unique case where one rabbi testifies that another rabbi argued a position with which he did not agree.
Section six: Rabbi Yohanan ben Nuri says that hailstones are treated like water. If they have been drawn in a vessel and then they were put into a mikveh, they render the mikveh invalid.
Section seven: This section explains how any of these substances can raise a mikveh up to the requisite quantity.