Before Birkath Hammazon (grace after meals) one must be particular to do Mayim Aharonim (literally "the last waters") by washing ones fingers. Only a small amount of water must be used for this and the fingers should be kept together but separated from the thumb, and the fingers should point downwards.
Mayim Aharonim must be poured by a human being (generally the person himself) over the fingers, into a vessel and not onto the ground (earth). However, if a vessel cannot be found it may be done onto the (paved/tiled) floor. Mayim Aharonim may not be done with hot water, and some say it must actually be cold, and it is appropriate to follow this ruling.
If water cannot be found to do Mayim Aharonim, it can be done with any other liquid that is suitable for drinking, even wine, since there is no alternative.
(See Ben Ish Hai, Shanah Rishonah, Parashath Shelah Lekha, Othioth Waw, Heth, Yod, Yod Aleph)
