Mishnah Yadayim 2:2: Regarding one who poured out the first [waters poured for washing] onto one place [i.e. the waters fell onto a certain area on the ground], and the second [waters poured for washing] onto another place, if a loaf of terumah falls into the first [waters], it is impure; and if [it falls] into the second [waters], it is pure. Regarding one who poured out the first and the second [waters] onto one place, if a loaf of terumah falls [into those waters], it is impure. If one poured out the first [waters], and finds [afterwards] a splinter or a pebble on his hands, his hands are impure [if he poured the second waters before removing them], since the latter [i.e. the second] waters only purify the waters on the hand [but not the waters on the splinter or pebble, which can then, in turn, render the hand impure once more]. Rabbi Shimon ben Gamliel says: anything produced from the water is pure [i.e. does not prevent hands from becoming pure if it is on them while they are being washed].

נָטַל אֶת הָרִאשׁוֹנִים לְמָקוֹם אֶחָד, וְאֶת הַשְּׁנִיִּים לְמָקוֹם אַחֵר, וְנָפַל כִּכָּר שֶׁל תְּרוּמָה עַל הָרִאשׁוֹנִים, טָמֵא, וְעַל הַשְּׁנִיִּים, טָהוֹר. נָטַל אֶת הָרִאשׁוֹנִים וְאֶת הַשְּׁנִיִּים לְמָקוֹם אֶחָד, וְנָפַל כִּכָּר שֶׁל תְּרוּמָה, טָמֵא. נָטַל אֶת הָרִאשׁוֹנִים וְנִמְצָא עַל יָדָיו קֵיסָם אוֹ צְרוֹר, יָדָיו טְמֵאוֹת, שֶׁאֵין הַמַּיִם הָאַחֲרוֹנִים מְטַהֲרִים אֶלָּא הַמַּיִם שֶׁעַל גַּבֵּי הַיָּד. רַבָּן שִׁמְעוֹן בֶּן גַּמְלִיאֵל אוֹמֵר, כֹּל שֶׁהוּא מִבְּרִיַּת הַמַּיִם, טָהוֹר:

Mishnah Yadayim 2:3: The hands may be rendered impure or pure up to the wrist. How so? If one poured the first [pouring] up to the wrist, and the second [pouring] beyond the wrist, and they [i.e. some of the waters flowed down and] ran back onto the hand, it is pure. If one poured the first and the second [pourings of water] beyond the wrist, and they ran back onto the hand, it is impure. If one poured the first over one hand, and then changed his mind and poured the second over both hands, they are impure. If one poured the first over both hands, and then changed his mind and poured the second over one hand, his hand is pure. If one poured over one hand, and then rubbed it against its fellow [hand], it is impure. If [one rubbed it] against one's head, or against a wall, it is pure. Four or five [people] may pour [water over their hands to wash them] alongside one another or [when their hands are] above one another, provided they be loose, so the waters can enter into them.

הַיָּדַיִם מִטַּמְּאוֹת וּמִטַּהֲרוֹת עַד הַפֶּרֶק. כֵּיצַד. נָטַל אֶת הָרִאשׁוֹנִים עַד הַפֶּרֶק, וְאֶת הַשְּׁנִיִּים חוּץ לַפֶּרֶק, וְחָזְרוּ לַיָּד, טְהוֹרָה. נָטַל אֶת הָרִאשׁוֹנִים וְאֶת הַשְּׁנִיִּים חוּץ לַפֶּרֶק וְחָזְרוּ לַיָּד, טְמֵאָה. נָטַל אֶת הָרִאשׁוֹנִים לְיָדוֹ אַחַת וְנִמְלַךְ וְנָטַל אֶת הַשְּׁנִיִּים לִשְׁתֵּי יָדָיו, טְמֵאוֹת. נָטַל אֶת הָרִאשׁוֹנִים לִשְׁתֵּי יָדָיו וְנִמְלַךְ וְנָטַל אֶת הַשְּׁנִיִּים לְיָדוֹ אַחַת, יָדוֹ טְהוֹרָה. נָטַל לְיָדוֹ אַחַת וְשִׁפְשְׁפָהּ בַּחֲבֶרְתָּהּ, טְמֵאָה. בְּרֹאשׁוֹ אוֹ בַכֹּתֶל, טְהוֹרָה. נוֹטְלִין אַרְבָּעָה וַחֲמִשָּׁה זֶה בְצַד זֶה אוֹ זֶה עַל גַּבֵּי זֶה, וּבִלְבַד שֶׁיְּרַפּוּ שֶׁיָּבֹאוּ בָהֶם הַמָּיִם: