Liturgy for Yadayim 1:1
מֵי רְבִיעִית נוֹתְנִין לַיָּדַיִם, לְאֶחָד, אַף לִשְׁנַיִם. מַחֲצִית לֹג, לִשְׁלשָׁה אוֹ לְאַרְבָּעָה. מִלֹּג, לַחֲמִשָּׁה וְלַעֲשָׂרָה וּלְמֵאָה. רַבִּי יוֹסֵי אוֹמֵר, וּבִלְבַד שֶׁלֹּא יִפְחֹת לָאַחֲרוֹן שֶׁבָּהֶם מֵרְבִיעִית. מוֹסִיפִין עַל הַשְּׁנִיִּים וְאֵין מוֹסִיפִין עַל הָרִאשׁוֹנִים:
A quarter [of a <i>log</i>, a specific unit of volume] of water is to be poured onto the hands, for [the ritual washing of the hands for] one person, and even for two. Half of a <i>log</i> [is to be poured from] for three or four. And from [a vessel containing] one <i>log</i> [of water], five or ten or even one hundred [people may wash their hands]. Rabbi Yose says: but only provided there not be less than a quarter [of a <i>log</i> remaining] for the last one of them [to wash]. One may add [water, by pouring it onto the hands past where it had fallen] on the second [pouring of water; i.e. on a third pouring, one can pour past where the waters fell on the second pouring]. But one may not add on the first [pouring; i.e. on the second pouring, one may not pour past where the waters fell on the first pouring].