6הַטָּמֵא שֶׁיָּרַד לִטְבּל סָפֵק טָבַל סָפֵק לֹא טָבַל וַאֲפִלּוּ טָבַל סָפֵק יֵשׁ בּוֹ אַרְבָּעִים סְאָה סָפֵק אֵין בּוֹ. שְׁנֵי מִקְוָאוֹת אֶחָד יֵשׁ בּוֹ אַרְבָּעִים סְאָה וְאֶחָד אֵין בּוֹ וְטָבַל בְּאֶחָד מֵהֶן וְאֵין יָדוּעַ בְּאֵיזֶה מֵהֶן טָבַל סְפֵקוֹ טָמֵא לְפִי שֶׁהַטָּמֵא בְּחֶזְקָתוֹ עַד שֶׁיִּוָּדַע שֶׁטָּבַל כָּרָאוּי. וְכֵן מִקְוֶה שֶׁנִּמְדַּד וְנִמְצָא חָסֵר בֵּין שֶׁהָיָה הַמִּקְוֶה בִּרְשׁוּת הָרַבִּים בֵּין שֶׁהָיָה בִּרְשׁוּת הַיָּחִיד כָּל הַטָּהֳרוֹת שֶׁנַּעֲשׂוּ עַל גַּבָּיו לְמַפְרֵעַ טְמֵאוֹת עַד שֶׁיִּוָּדַע זְמַן שֶׁנִּמְדַּד בּוֹ וְהָיָה שָׁלֵם. בַּמֶּה דְּבָרִים אֲמוּרִים כְּשֶׁהָיְתָה הַטְּבִילָה מִטֻּמְאָה חֲמוּרָה. אֲבָל אִם טָבַל מִטֻּמְאָה קַלָּה כְּגוֹן שֶׁאָכַל אֳכָלִין טְמֵאִין אוֹ שָׁתָה מַשְׁקִין טְמֵאִין אוֹ בָּא רֹאשׁוֹ וְרֻבּוֹ בְּמַיִם שְׁאוּבִין אוֹ שֶׁנָּפְלוּ עַל רֹאשׁוֹ וְעַל רֻבּוֹ שְׁלֹשֶׁת לוֹגִין מַיִם שְׁאוּבִין. הוֹאִיל וְעִקַּר דְּבָרִים אֵלּוּ מִדִּבְרֵיהֶן הֲרֵי סְפֵקוֹ טָהוֹר כְּמוֹ שֶׁבֵּאַרְנוּ. וְאַף עַל פִּי שֶׁנִּסְתַּפֵּק לוֹ אִם טָבַל אוֹ לֹא טָבַל אוֹ שֶׁנִּמְצָא הַמִּקְוֶה חָסֵר לְאַחַר זְמַן וְכַיּוֹצֵא בִּסְפֵקוֹת אֵלּוּ הֲרֵי זֶה טָהוֹר:
In all the following situations, when an impure person descends to purify himself and: a) there is a doubt whether he immersed or did not immerse, b) even if it was known that he immersed, but there is a doubt whether the mikveh contained 40 se'ah or not, or c) there were two mikveot, one containing 40 se'ah and one that did not contain 40 se'ah, he immersed in one of them and did not know in which one he immersed, he is impure because of the doubt. The rationale is that we presume that the impure person is impure until it is certain that he immersed in the proper manner. Similarly, if a mikveh was measured and it was discovered that it did not contain the required amount of water, whether the mikveh was located in the public domain or a private domain, all of the pure articles that were immersed in it are considered as impure retroactively until a time when it was measured and it was complete. When does the above apply? When the immersion was intended to purify the person or the article from severe impurity. When, however, the immersion was because of a light impurity, e.g., one ate impure foods or drank impure beverages, his head and the majority of his body entered drawn water, or three lugim of drawn water fell on his head and on the majority of his body, since the primary aspect of these types of impurity are Rabbinical in origin, he is pure despite the doubt, as we explained. Even though the person is in doubt whether he immersed or not, the mikveh in which he immersed was discovered to be lacking afterwards, or other doubts of this nature arise, he is pure.