Mishnayos Mikvaos Perek 6 Mishnah 6

If there was a broken [earthenware] vessel in the mikveh and utensils were immersed in it, they become clean from their [former] uncleanness but are again rendered unclean because of the earthenware vessel. But if water flowed above it in any quantity, they are clean. If [water of] a spring flowed forth from an oven and a man went down and immersed himself in it, he is clean but his hands become unclean. But if [the water was as] high above the oven as the height of his hands, his hands also are clean.

גִּסְטְרָא שֶׁבַּמִּקְוֶה וְהִטְבִּיל בָּהּ אֶת הַכֵּלִים, טָהֲרוּ מִטֻּמְאָתָן, אֲבָל טְמֵאִים עַל גַּב כְּלִי חֶרֶס. אִם הָיוּ הַמַּיִם צָפִים עַל גַּבָּיו כָּל שֶׁהֵן, טְהוֹרִין. מַעְיָן הַיּוֹצֵא מִן הַתַּנּוּר וְיָרַד וְטָבַל בְּתוֹכוֹ, הוּא טָהוֹר וְיָדָיו טְמֵאוֹת. וְאִם הָיוּ עַל גַּבָּיו רוּם יָדָיו, אַף יָדָיו טְהוֹרוֹת: