The eminent Muslim scholar, Sheikh Muhammad Al-Hanooti, member of the North American Fiqh Council, states: “A Muslim is allowed to drink water in any position he/she likes. The Prophet (peace and blessings be upon him) was seen drinking Zamzam water standing up. The great Companions of the Prophet (peace and blessings be upon him) used to drink standing up. Both the two directions are advocated by narrations to make it optional. In one, the Prophet (peace and blessings be upon him) told people not to drink standing up. There are two opinions in interpretation of this hadith. Some scholars take this hadith literally and say that drinking while standing up is haram. However, other responded, saying that sighting the Prophet (peace and blessings be upon him) drinking during Hajj while he is standing up is an answer. There is no room when he does that openly to say that the ruling is exceptional to him. We don’t have an evidence for exceptionality. It is possible to say that it is better for you to drink sitting, but notstanding.”
Sheikh `Atiyyah Saqr, former head of Al-Azhar Fatwa Committee, adds:
Imam Muslim reported that the Prophet (peace and blessings be upon him) said “None of you should drink while standing; and if anyone forgets, he must vomit.” It was the Prophet’s habit to drink while sitting. However, it is reported by al-Bukhari and Muslim that he was given Zamzam water and he drank it while standing. Reconciling these two seemingly conflicting hadiths is possible and none of them abrogates the other. Drinking while sitting is desirable but not obligatory and that is why the Prophet sometimes drank while standing to explain that doing so is permissible. Yet, it is better to drink while sitting. It is also authenticated that some of the Prophet’s Companions, particularly the Rightly Guided Caliphs, drank while standing.”