Reference for Makhshirin 2:4

הַטּוֹרֵף אֶת גַּגּוֹ וְהַמְכַבֵּס אֶת כְּסוּתוֹ וְיָרְדוּ עֲלֵיהֶן גְּשָׁמִים, אִם רֹב מִן הַטָּמֵא, טָמֵא. וְאִם רֹב מִן הַטָּהוֹר, טָהוֹר. מֶחֱצָה לְמֶחֱצָה, טָמֵא. רַבִּי יְהוּדָה אוֹמֵר, אִם הוֹסִיפוּ לְנַטֵּף:

[If] one plasters his roof or launders his clothing and rain fell into them [the waste water used for those activities]: [If] most [of the mixture] is from the impure [waste water] it is impure; and if most it is from the pure [rain water] it is pure; [if] it is half and half it is impure. Rabbi Yehudah says: If [the volume of] the dripping increased.

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