Yadayim, Chapter Two, Mishnah Three
1) Hands become unclean and are made clean as far as the joint.
2) How so? If he poured the first water over the hands as far as the joint and poured the second water over the hands beyond the joint and the latter flowed back to the hands, the hands are clean.
3) If he poured the first and the second water over the hands beyond the joint and they flowed back to the hands, the hands remain unclean.
4) If he poured the first water over one of his hands and then changed his mind and poured the second water over both his hands, they are unclean.
5) If he poured the first water over both his hands and then changed his mind and poured the second water over one of his hands, his one hand becomes clean.
6) If he poured water over one of his hands and rubbed it on the other hand it remains unclean.
7) If he rubbed it on his head or on the wall it is clean.
8) Water may be poured over the hands of four or five persons, each hand being by the side of the other, or being one above the other, provided that the hands are held loosely so that the water flows between them.
Section one: For matters of purity, the hand goes up to the “joint.” There are two explanations of this. The first is the middle joint of the fingers and the second is the joint where the fingers join the hand. Below, I will simply use the word “joint.”
Section two: The mishnah now explains some ramifications of this ruling. If he pours water the first time over his hands as far as the joint and then the second time beyond the joint, and the second water goes back onto his hand, his hands are pure. This is because beyond the joint the hand is not impure. So the second water was not made impure by going beyond the joint.
Section three: In this case he pours both beyond the joint and then the water flows back onto his hands. His hands remain impure because the first water that went beyond the joint wasn’t purified by the second water that was also beyond the joint, because this water is only purified when it is on the hand. When the water goes back it defiles his hand again.
Section four: The mishnah now deals with a different subjectone who changes his mind about how many hands to wash. If the first time he washes, he washes only one hand and then the second time he washes both hands and the water from the second hand goes on to the first hand, the first hand is defiled. This is because the water that went on the second hand was only there for the first time.
Section five: However, in the opposite case, where he first washed both hands and then only one, the one hand that was washed twice is pure.
Section six: If he washes one hand (even twice) and then rubs it on the other, the water becomes impure on the second hand. This water then goes back and defiles the first hand.
Section seven: However, if he rubs his hands on his head or the wall, the water is not defiled. The water that then goes back onto his hands does not defile them again.
Section eight: One can pour water over several people’s hands at once and we are not concerned that one person’s hands would defile another person’s. The only important rule is that the hands shouldn’t be tightly clenched with one another. Water must be allowed to flow in-between.