I have come across the following Hadīth:
Abū Hurayrah reports from the Prophet: No one from amongst you should drink water while standing. Whoever forgets should throw up. (Muslim: Kitābu’l-Ashribah)
Does this mean that drinking water while standing is absolutely prohibited?
Drinking water while sitting down is part of the social etiquette Islam teaches its followers. One should try to observe this etiquette whenever it is possible for him. However, if a person does not do so, he will not be punished since this directive is not part of the Islamic Sharī‘ah. It is known that the Prophet (sws) drank water while standing up as well:
‘Umar Ibn Shu‘ayb reports from his grandfather: I saw that the Prophet (sws) used to drink water while standing as well as sitting. (Tirmadhī: Kitābu’l-Ashribah)
Similarly, there are a number of other Ahādīth which narrate that many companions of the Prophet (sws) also used to follow both practices.
The Hadīth you have referred to is not only Mawqūf (a sort of weakness in its chain of its narrators), according to some scholars of Hadīth, but also cannot be accepted in the presence of a number of Ahādīth in which drinking water while standing is regarded as perfectly allowable. After all, the Prophet (sws) cannot simultaneously give two opposite directives.
In my opinion, it seems that in the Hadīth of Abū Hurayrah and in other Ahādīth which contain such severity on drinking water while standing, either there must have been other details which have failed to reach us or the narrators misunderstood what the Prophet (sws) had actually said.