515. Mayim Rishonim vs. Mayim Achronim

Brachos 6:15

Let’s say that a question arises concerning the water that one used to wash his hands  - was it used for other work, did it contain the requisite volume, was it ritually clean, etc. – or a doubt arises as to whether one washed his hands at all. In any these cases, one’s hands are considered purified. Whenever a question arises about the ritual purity of one’s hands, the hands are considered pure.

Brachos 6:16

When washing before a meal, one should raise his hands so that that water will not flow back down past his wrists. If the water were to roll back, it would render his hands impure. Conversely, when one washes after a meal, he should hold his hands downward so that the residue of the salt gets rinsed off his hands. Before eating, one may wash his hands into a receptacle or onto the ground; after eating, one should only wash his hands into a receptacle. Before eating, one may wash with hot water or with cold water. One should not wash with scalding water after eating; this will not cleanse sufficiently because a person cannot rub his hands together with it. Warm water may be used for washing after the meal.