How much water should be used for Mayim Acharonim?

The Shela Ha’kadosh (a”h) states that one should not lean during the reading of the Hagadah at the Seder. Even though generally one may lean at the Seder even at the points when Halachah does not require leaning, it would be inappropriate to lean while performing the Mitzvah of reading the Hagadah, during which one should sit with a sense of awe and reverence.The Ben Ish Chai (a”h), in Parshat Lech-Lecha, writes that one should ensure to use only a small amount of water when washing Mayim Acharonim (the washing done before Birkat Hamazon). He explains that the water of Mayim Acharonim is associated with the “Sitra Achara” (literally, “the other side”), the forces of impurity, and we therefore should use small amounts of water in order not to strengthen the hostile spiritual forces.

He then proceeds to address the case of a person whose hands are dirty, such that a small amount of water would not suffice to clean them. In such a case, he writes, one should thoroughly wash his hands – and, if necessary, his mouth – normally, at the sink, with the intention of continuing to eat. Since he intends to continue eating after washing, this washing will not be considered Mayim Aharonim, and thus he may use as much water as he needs to clean his hand and face.

He should then return to the table, eat a morsel of bread or other food, and then wash Mayim Acharonim with a small amount of water. This way, he is able to properly clean his hands while still using only a small amount of water for Mayim Acharonim.

Likewise, one should refrain from drinking during the reading of the Hagadah. A person who experiences excessive thirst may drink some water and a person who feels very frail may even drink coffee; otherwise, however, one should refrain from drinking during the reading of the Hagadah, due to the sanctity of the moment, which demands an aura of reverence.