As a method of execution:

In Europe, drowning was used -- more often than hanging, even -- as capital punishment, at least for a time. In fact, during the Middle Ages, a sentence of death was read using the words "cum fossa et furca," or "with drowning-pit and gallows." Commonly, women who were convicted of theft were drowned. Furthermore, drowning was used as a way to determine if a woman was a witch. The idea was that witches would float and the innocent would drown. For more details, see trial by drowning. It is understood that drowning was used as the least brutal form of execution, and was therefore reserved primarily for women, although favorable men were executed in this way as well.