The Volume of Water for Mayim Achronim
Q. How much water is needed for Mayim Achronim?
A. The Beis Yosef (OC 181) writes that there is no specific amount of water for mayim achronim, but one must pour enough water to wash the fingers up to the second knuckle and the thumb until the first knuckle. The Mishnah Berurah (181:10) explains that one need not wash beyond this point, since the upper parts of the fingers do not ordinarily touch food. The Mishnah Berurah strongly condemns the practice of pouring a few drops of water on the fingers and then rubbing them together. Rather, enough water should be poured on the fingers to cleanse them. Although most poskim follow the ruling of the Beis Yosef, the Mishnah Berurah (181:19) also records the custom of the Vilna Gaon to use a revi’is (approx. 3.3 oz) of water for mayim achronim.
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