Bathing on Shabbos
5. It is permissible on Shabbos to stand on a river bank and wash one's hands in the river, and one would not be transgressing a prohibition if one transported the water on one's hands, from the river onto its bank; this is because both the river and its bank have the status of a "carmelis," and it is permissible to carry something from one "carmelis" to another, as long as the distance carried is less than four "amos" (1). One should be careful to dry one's hands well before walking a distance of four "amos".
(1) Opinions among the authorities as to the exact length of an "Amah" ("cubit") range between 48 and 60cm (20 to 24 inches).
Halacha-Yomi, Copyright (c) 2002 Project Genesis, Inc.