The Halacha requires washing Mayim Aharonim at the conclusion of the meal, before Birkat Hamazon. The question was asked whether one may use moist towelettes, which are commonly distributed at the end of a meal in restaurants, for this obligation. This question can be answered only after reviewing the four reasons given for this obligation. According to the reason that it is to clean the hands for Birkat Hamazon, the towelette should be permitted. With regard to cleanliness, there is no difference whether one uses a traditional vessel with water or the towelette. Another reason for Mayim Aharonim was to remove traces of a certain salt called "Melech Sedomit", which was once common in the bread. If it would remain on the fingers, it was liable to be rubbed on the eyes and, Heaven forbid, cause blindness. If that is the reason, the towelette should be sufficient. There is yet another explanation, based on the Gemara in Masechet Yoma, that relates the story of someone who was once killed because he didn't do Mayim Aharonim and traces of food remained on his face. Again, if this is the reason, towelette can also effectively wipe the face.
However, there is a fourth reason for Mayim Aharonim, based on the Kabbalah, brought by Rav Haim Vital (1543-1620, Tsfat-Damascus) in the Sha'ar Ha'Kavanot. He writes that after a person eats, the Sitra Achra (the Satan) wants to prosecute the diner and claim that he doesn't deserve to eat because of his sins. This would cause the Heavenly court to open his books and investigate his merit. To avoid this, one must give a "bribe" to the Satan in the form of water with the residue of food from the fingertips. That is his portion and causes him to remain quiet. According to that reason, it is questionable whether the moisture in the towelette is sufficient. It could be argued that it is enough, since anyway, all the Poskim say that one should only use a small amount of water for Mayim Aharonim. Apparently a minute amount is sufficient. The fact that the moisture in the towelette is not water, but a chemical, is not a problem. Mayim Aharonim nay be performed with any liquid, including saliva, soda or juice.
Rabbi Gidon, in his new Sefer, Yoru Mishpatecha (Siman 20) discusses this question. He rules that ideally, if one has water, he should wash in the regular manner, since the Kaf Ha'Haim (Rav Yaakob Haim Sofer, Baghdad-Israel, 1870-1939) specifically formulated the Halacha that one should "pour" water over his hands. However, if he is travelling and does not have easy access to water, e.g. he is eating while driving in a car, he may use the towelette. This may also be considered "pouring". The Kaf Ha'Haim was only coming to exclude immersing one's hands in the water. However, it is problematic to use them on Shabbat, if he squeezes them. In any event, one should never be lenient and omit Mayim Aharonim, as the Poskim are very strict in this matter.
If one does not have access to water, he may use moist towelettes for Mayim Aharonim.