Questions on the Bartenura in Beitza 2:3

Question

After listing some points of disagreement between the schools of Shammai and Hillel in Beitza 2:1-2, the third mishna commences by presenting the following case:

ושוין שמשיקין את המים בכלי אבן לטהרן

They [the schools of Shammai and Hillel] agree that one can pour water into a stone vessel to purify it...

This cryptic statement is interpreted by the Bartenura as follows:

ושוין שמשיקין את המים בכלי אבן. מי שיש לו מים יפים לשתות ונטמאו, ממלא מהן כלי אבן שאינו מקבל טומאה ונותנן במקוה מים מלוחים או עכורים עד שנושקים מים למים, נמצאו אלו זרועים ומחוברים למי מקוה ובטלו אגבייהו וטהרו. ואין טהרה במקוה לשום אוכל ומשקה אלא למים בלבד, ולא בתורת טבילה אלא בתורת זריעה

They agree that one can pour water into a stone vessel: Somebody who has nice water to drink, which becomes impure, can fill a stone vessel (which cannot receive impurity) with it and place it in a body of salty or cloudy water until the water [in the vessel] and the water [in the miqveh] are touching. Thus, it [the water in the vessel] is "sown" and joined to the water of the miqveh, is nullified in comparison to it and is purified. One cannot use a miqvah [on yontef] to purify for food or for any drink except for water, and it is not through the torah of immersion but the torah of sowing.

My question is two-fold:

Firstly, what does the Bartenura mean when he speaks about "sowing" (זרוע, תורת זריעה)? In what sense is the water being "sown"?

Secondly, why is it necessary for the water of this miqveh to be salty or cloudy?

Answer 1

The answer to your first question about the meaning of the expression "sowing" can be found in Rashi in the gemara Bechoros 22a (fruits of my learning in this program!):

One puts the vessel containing the impure water in the mikveh until the water of the mikveh passes over the mouth of the vessel and makes contact with the water that is in the vessel. And even though food and drink cannot be purified in a mikveh, water can be purified through this contact because it is like they are being sown [in the ground] and then retrieved. Because sowing purifies something which is impure, as the Mishnah in Terumos (9,7) teaches "plants of terumah which became impure, but were then were planted in the ground, become purified". I found this explanation in the responsa of Rabbeinu Gershon.

The answer to your second question - why the Bartenura explains that the water of the mikveh is cloudy or salty - can be found in the Tosfos Yom Tov on this Mishnah, who says;

because if the mikveh is not salty or cloudy, why does he need to purify the water? He already has drinking water available!