Rambam - 1 Chapter a Day

See Hilchot Sha’ar Avot HaTum’ah 14:1.

As explained above, if three lugim of drawn water fall into a mikveh containing less than 40 se’ah of acceptable water, they disqualify it. If, however, there are less than three lugim or more than 40 se’ah of acceptable water, the mikveh remains acceptable. As a preface to the entire chapter which deals with questions of uncertainty, the Rambam clarifies that as long as one is not certain that the mikveh has been disqualified, it is considered acceptable.
According to the Rambam, the reason for the leniency is that the concept that drawn water disqualifies a mikveh is a Rabbinic decree and we follow the general principle: “Whenever there is a doubt regarding a question of Rabbinic Law, we rule leniently” (see Turei Zahav 201:81).

We assume that the drawn water fell into the mikveh that contained the required measure and thus would not be disqualified by the drawn water. Hence the other mikveh is also acceptable. Although there is no empirical basis for this assumption, since the doubt about the acceptability of the mikveh involves a question of Rabbinic Law and there is a possibility that the water fell into the acceptable measure, we follow this approach. Note parallels in Hilchot Terumot 13:14.

Hence, since there is no way of determining which mikveh the water fell into, they are both disqualified, for there is no reason to favor one over the other and one is certainly invalid (Siftei Cohen 201:142).

Needless to say, this law also applies when the mikveh contained less than 40 se’ah of acceptable water. See the conclusion of the following halachah.

The Kessef Mishneh maintains that the rationale for accepting the mikveh here is different than that in Halachah 1. The concept stated there — that when there is a doubt whether water is drawn or not, we rule leniently — applies only in an instance when there is already an existing mikveh. If the mikveh was empty, it is considered acceptable because of a different rationale: that when there is no factor that indicates that it is likely to have been filled in an unacceptable manner, we operate under the presumption that any mikveh that is discovered is acceptable (Tosefta, Mikveot 2:1). The Shulchan Aruch, Yoreh De’ah 201:69 accepts the Rambam’s ruling. The Rama, however, maintains that a mikveh of drawn water is unacceptable according to Scriptural Law. Therefore, he maintains that the present situation is comparable to a doubt arising with regard to a point of Scriptural Law, in which instance, a stringent ruling is called for.

Which is acceptable, because a pipe is not a container and it does not disqualify the water. See Chapter 6, Halachah 2.

I.e., a mill turned by water. The mill is considered as a k’li and disqualifies the water that passes through it.

In the previous halachah, there was a possibility that the mikveh had been filled by drawn water, but there is no evidence that this was what had happened. Here, when the disqualifying factor is next to the mikveh and there is a likelihood that the water came from it, the Sages were not willing to allow the leniency. The Siftei Cohen 201:144 explains that this is speaking about an instance when it is more likely that the water came from the mill, e.g., the mill is closer to the mikveh. Hence, that possibility is given more weight.
The Rabbis have questioned this ruling, because although there is a possibility that the water came from the mill, there is no evidence of such. It is just as possible that it came from the pipe. Hence, since the matter is one of Rabbinic Law, there is room for leniency. The Turei Zahav 201:83 explains that the rationale mentioned by the Kessel Mishneh, that we operate under the presumption that the mikveh is acceptable does not apply in this instance, since a factor that could disqualify the mikveh is present.

I.e., more than 20 se’ah.

This law applies even according to the authorities who maintain that a mikveh filled with drawn water is unacceptable according to Scriptural Law. In this instance, since there already is the majority of an acceptable mikveh, according to Scriptural Law, the drawn water is considered as insignificant. Hence, when it is not certain that drawn water was in fact added to the mikveh, we rule leniently.

In the Talmudic era—and in the Rambam’s time as well—the term mikvaot did not refer to a special ritual bath, as it does today. Instead, it referred to any pool or collected body of water.

I.e., if the status of a pool of water is unknown, we rule stringently. If, however, a mikveh is known to be acceptable — as the mikveot, ritual baths, used today — there is no problem in relying upon it [see the Rambam’s Commentary to the Mishnah (Mikveot 8:1)].

And may be used by a woman to purify herself from nidah impurity. There is no need to verify the status of the mikveh (ibid.).
The Kessel Mishneh states that this ruling applied only in the Talmudic era when Bretz Yisrael was inhabited primarily by Torah observant Jews. In eras when that is not the case, there is no difference in this regard between Bretz Yisrael and the Diaspora.

For in previous eras, it is unlikely to have pools of water in outlying areas that did not come from rain water or a natural stream. Indeed, the Siftei Cohen 201:150 states that even in the Diaspora, if it is apparent that a pool came about through natural means, it is acceptable for immersion.

I.e., he immersed, but he was unsure if his entire body was immersed as required.

The Turei Zahav 201:85 suggests that this law applies even when it is known that the mikveh once contained the required measure.

Since the person is known to be impure, he cannot change his status unless he immerses in a manner that leaves no doubt that he is pure.

With regard to contracting ritual impurity, there is a difference between the public domain and a private domain, as explained in Hilchot Sha’ar Avot HaTum’ah 14:1, 16:1-2. Nevertheless, with regard to purification, no such distinction is made.

The rationale is the same as in the first clause. Since the articles were known to be impure, their status does not change until it is known with certainty that they were immersed in an acceptable mikveh. In this instance, since the mikveh was discovered to be unacceptable, the status of all the articles immersed in it from the last time that it was measured is thus deemed questionable.

The intent is a person who contracted impurity through contact with a source of impurity. This includes even a source of impurity of Rabbinic origin (Ra’avad, Kessef Mishneh, based on Taharot 4:7, 11).

See Hilchot Sha’ar Avot HaTum’ah 8:10.

Ibid. 9:1.

For this is considered an ordinary instance of a doubt regarding a Rabbinic injunction.

The Merkevet HaMishneh states that this — like the final clause of the halachah — is speaking about a mikveh that is unacceptable because its water was drawn. Others maintain that this is talking about a mikveh that does not contain 40 se’ah.

Either terumah or sacrificial foods.

Since it is possible that his immersion was unacceptable, his status might not have changed and thus he would impart impurity to the articles that he touched. On the other hand, since he is not definitely impure, the status of the articles is questionable. They are not considered as impure and consigned to being burnt (because it is forbidden to burn terumah or sacrificial foods that are acceptable), nor are they considered pure and eaten. Instead, they are left until they definitely contract impurity or are disqualified for other reasons.

Since he immersed in both mikvaot, he obviously purified himself. Moreover, he is not considered impure, because he immersed his body in drawn water. Since the impurity of drawn water is merely a Rabbinic stringency and it is not known with certainty that he immersed in it after purifying himself, it is assumed that he immersed in the acceptable mikveh last.

The same ruling that applied to them originally still applies. Even if the person immersed in the acceptable mikveh originally and then in the mikveh filled with drawn water, the foods that he touched originally do not become impure because of the contact with the second· group of foods. Although the second group becomes impure, their impurity does not impart impurity to other foods, because it is only a Rabbinic safeguard.

They are definitely impure. If the first immersion was in the acceptable mikveh, the second immersion was in drawn water and the person became impure. He then imparts impurity to the foods he touches. If the first immersion was in the invalid mikveh, the articles he touched afterwards also become impure. Moreover, since their impurity stems from contact with a severe type of impurity, they also impart impurity to other foods with which they come in contact. Therefore they impart impurity to the second batch of foods.

In Halachah 6.

I.e., the fact that he contracted a light impurity and immersed does not change any of the logic mentioned in note 30.

For the reasons explained in Halachah 6.

Because as in the first situation mentioned in this halachah, it is not known whether or not the person’s immersion was acceptable.

This follows the same rationale as the ruling in the first clause. The first batch of foods should be burnt because if the first immersion was acceptable, the second was not and the foods touched afterwards contracted impurity and imparted that impurity to the first batch. And if the first immersion was unacceptable, the person became impure due to the immersion in drawn water and he imparts that impurity to the foods he touches.

For the reasons stated in note 27.

Because it is a questionable situation regarding a Rabbinic safeguard, as stated in Halachah 6.

In the first clause above.

Which is merely a Rabbinic safeguard. Hence, when a doubt arises in such a situation, we rule leniently.

As explained with regard to the last clause of the previous halachah, this is a situation where a doubt has arisen regarding whether a person entered drawn water or not. Hence he is considered as pure.

Since he entered both pools. Since the acceptable pool did not contain 40 se'ah, there is no possibility that he was purified after entering the pool of drawn water.