Study Niddah folio 3A with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
The Talmud explains their reasoning: And both tanna’im derived their respective opinions only from the case of a woman suspected by her husband of having been unfaithful [sota], who is forbidden to have sex with her husband just like a definite adulteress.
The Rabbis hold: This case of a mikveh is like the case of a sota. Just as in the case of a sota it is uncertain whether she was actually unfaithful, and nevertheless the Torah rendered her like one who definitely committed adultery in that she is forbidden to her husband until she drinks the water
The Talmud raises a difficulty: If the halakhot of the mikveh are derived from those of a sota, then one can say that it should be like the halakha of a sota in another respect: Just as a sota who is suspected of having been unfaithful in a public domain is considered pure, i.e., she does not unde
The Talmud answers: How can these cases be compared? One cannot apply the halakha of a sota in a public domain to any other case. There, the reason why a sota is treated as having definitely been unfaithful is due to her seclusion with another man. And as a proper seclusion in the public domain is
The Talmud comments: And if you would say that the guiding principle in any case of uncertainty involving impurity in a public domain is that it is ritually pure, and therefore all items immersed in a mikveh situated in the public domain should be pure even if there is uncertainty about its status