נוטל אדם ידיו שחרית ומתנה עליהם כל היום אפי' שלא בשעת הדחק ובלבד שלא יסיח דעתו מהם (ולא יטנפם) (טור) ואם מים מצויים לו טוב שיחזור ויטול ידיו אבל לא יברך: הגה והא דמהני תנאי דוקא בנטילה שאינה צורך אכילה דומיא דנטילת שחרית אבל אם נוטל לצורך אכילה לא מהני תנאי באותה נטילה: (ב"י בשם הר"י):

A person may wash his hands in the morning and stipulate that the washing covers him for the entire day, even not in a time of pressing need, provided he does not have a lapse of attention regarding them (and does not soil them) (Tur). If water is readily available it is good to wash again, but he should not recite a blessing. Rema: The stipulation is only effective for washing that is not needed for eating, similar to the morning handwashing; but if one is washing for the purpose of eating, a stipulation does not help for that washing. (Beit Yosef in the name of Ri)

One who is in the middle of a meal and remembers that he touched his thigh, upper leg, or the covered parts of the body, or that he scratched his head and similar things (and soiled areas that have accumulated perspiration residue) he must wash his hands again and recite the blessing over handwashing.