Editing Snow (section)

== The Alter Rebbe's Instruction ==
As support for his words, the Tzemach Tzedek brings that the Alter Rebbe gave similar instruction to make a mikvah by first removing the water from the mikvah and bringing snow to put into the empty mikvah. Afterwards, they would heat the bathhouse until the snow melted and became forty seah of water.

However, there is a distinction between making a mikvah with snow versus ice; when making a mikvah with ice, there's no need to empty the mikvah, since ice is a controversial permissibility when used independently and not as an addition to an existing mikvah. According to the Rambam it's invalid, so it's better to throw it into the mikvah with the previous water of questionable kashrus, even though others hold this isn't done properly, since either way the mikvah isn't completely kosher according to all opinions, and the sides of doubt are equal. In contrast, before adding snow to the mikvah, which makes it kosher according to all Rishonim, the mikvah water must be completely emptied, and the snow placed into the empty pit.