Drinking water in one breath is permissible and there is nothing wrong with it; however, it is desirable and would be better for one to drink water in three breaths. It is reported by AnasibnMalik that the Prophet (peace and blessings be upon him) used to take three breaths while drinking. (Agreed upon)
Moreover, what is disliked is breathing into the vessel while drinking, since the Prophet (peace and blessings be upon him) forbade this unhealthy habit.
Sheikh M. S. Al-Munajjid, a prominent Saudi Muslim lecturer and author, states that:
abu Sa`id Al-Khudri narrated that the Prophet (peace and blessings be upon him) forbade breathing into one’s drink. A man said to him, “O Messenger of Allah, my thirst is not quenched in one breath.” The Messenger of Allah (peace and blessings be upon him) said to him: “Remove the cup from your mouth, then take a breath.” He said, “What if I see specks in it?” He said, “Then pour them out.” (At-Tirmidhi)
Sheikh Al-Albani said, discussing what we learn from this hadith:
It is permissible to drink in one breath, because the Prophet (peace and blessings be upon him) did not denounce the man when he said, “My thirst is not quenched in one breath.” If drinking in one breath had not been permissible, the Prophet (peace and blessings be upon him) would have explained that to him, and would have said, for example, “Is it permissible to drink in one breath?” That would have been more appropriate than saying, “Remove the cup from your mouth…” if that had not been permissible.
What he said indicates that it is permissible to drink in one breath, and that if the person wants to take a breath, he should do so outside the vessel. This is what is clearly stated in the hadith of Abu Hurairah (may Allah be pleased with him), who said: “The Messenger of Allah (peace and blessings be upon him) said: ‘When any one of you drinks, let him not breathe into the vessel. If he wants to take a breath, then let him remove the cup from his mouth, then if he wants to drink more he may do so.” (Al-Bukhari)
Moreover, Al-Hafizh said: Imam Malik used this as evidence to indicate that it is permissible to drink in one breath. IbnAbiShaibah narrated from Sa`idIbn Al-Musayyib and a group of scholars that doing so is permissible. `Umaribn `Abd Al-`Azeez said: “What he forbade was breathing into the vessel, but if a person does not breathe into the vessel, if he wishes he may drink in one breath.”
Furthermore, what was said above about it is being permissible to drink in one breath, does not contradict the fact that the Sunnah is to drink in three breaths. Both are permissible, but the latter is preferable, because of the hadith of AnasIbnMalik (may Allah be pleased with him) who said: “When he drank, he would take a breath three times, and he said, that is more enjoyable and healthier.” (Muslim)