Mikvaos, Chapter 3, Mishnah 3. This chapter revolves around the rabbinic takanah that three lugin of mayim she'uvim, drawn water, falling into a mikveh that does not yet hold forty se'ah of mei geshamim, invalidate it. The previous mishnah discussed a mikveh into which three lugin had fallen, how such water can be repaired, and at what point we are permitted to consider the psul gone and the water restored to the status of a valid mikveh. Our mishnah presents a different picture entirely. Here we are not speaking of three lugin that fell into good rainwater. Here the pit itself was filled with drawn water from the start.
Our mishnah opens with a cistern that has been filled entirely with drawn water, "bor shehu molei mayim she'uvim." Numbers will make the case easier to picture. Say the pit contains twenty se'ah of mayim she'uvim, water wholly unusable for a mikveh. Then "v'ha'ama," an irrigation channel, directs mei geshamim into the pit, while at the far end there is an opening through which the water escapes, "v'yotzim mimenu." Fresh rainwater pours in continuously and the mixture drains out continuously. Our question is when we may conclude that the drawn water has been washed out and that what sits in the pit is now rainwater suitable for tevilah.
The mishnah rules: "l'olam hi b'psulah," the pit permanently retains its invalid status, "ad sheyitchashev shelo nishtayer min harishonim shlosha lugin," until one can calculate that there do not remain from the original water three lugin.
How is that calculation made? Continue with our numbers. Twenty se'ah of drawn water were there, and let us say forty se'ah of rainwater have since entered through the channel. The pit now contains sixty se'ah, of which one third is she'uvim and two thirds are valid rainwater. Since the water inside is mixed, every drop leaving the outlet is assumed to leave in that same proportion: two parts fit water for every one part drawn water. Therefore we must wait until enough water has flowed out that a full third of the departed water equals the original twenty se'ah, which means sixty se'ah must exit the pit. At that point we may assume that the twenty se'ah of she'uvim were included in what left, and the pit now holds water free of any concern of three lugin. In truth, slightly less than sixty se'ah will already suffice, because we do not need the drawn water to disappear altogether; we need only that what remains of it be less than three lugin.
The mishnah now turns to a series of cases in which the three lugin arrive in the mikveh, but not in one single stream from one single place. "Shnayim shehein matilin l'mikveh," two people are putting drawn water into a mikveh that does not yet contain forty se'ah, "zeh log umechtzah v'zeh log umechtzah," this one puts in a log and a half and that one puts in a log and a half. Together they amount to three lugin, but neither of them contributed the full measure.
"O hasochet es k'suso," or a person who squeezes out his clothing. Drawn water is not the only pesul; a second one exists, tefisas yedei adam, water that arrives in the mikveh by way of human handling. Water absorbed in a garment need not be she'uvim at all, yet once someone squeezes the cloth and drives the water out of it, that water enters the mikveh through a human act, and three lugin of it likewise ruin a mikveh holding less than forty se'ah of rainwater. Here, then, the man wrings his garment "umattil mim'komos harbei," the drops falling into the mikveh from numerous points along the fabric. The full three lugin arrive, yet not from a single spot.
"V'ham'areh min hatzartzur," and one who pours from a tzartzur, a vessel fitted with several spouts, "umattil mim'komos harbei." He is not pouring from one spout alone; the water leaves through three different openings at once.
Regarding all three of these situations, the mishnah records a dispute. Rabbi Akiva pronounces the mikveh fit, "Rabbi Akiva machshir," having received a mesorah to this effect, while "v'chachomim poslin," the Chachomim hold that the mikveh is ruined.
Rabbi Akiva then explains his position. "Lo amru," the language of the Chachomim was never "matilin" in the plural, which would suggest water entering from a number of places, "ella matil," a single act of pouring from a single place. Since our cases all involve water arriving from several sources, from separate spouts or from separate spots on the garment, the takanah of three lugin was never applied to them at all. The disqualification is only rabbinic, and a rabbinic decree is limited to the precise circumstances in which it was stated.
The Chachomim responded, "omru lo": "lo kach v'lo kach amru," the tradition employed neither of those formulations, not the plural and not the singular, "ella shenoflu," but rather spoke of three lugin having fallen into the mikveh. Once that is the wording, whether the water arrived from a single opening or from a dozen is beside the point; what matters is only that three lugin got in. And in every one of the cases listed, three lugin did fall into the mikveh, so the mikveh is pasul.
One qualification is worth noting. The decree is not without boundaries even in the view of the Chachomim, and several leniencies concerning three lugin entering a mikveh will be taught in the mishnah that follows.