Praise be to Allah.
There is nothing in the Prophet’s Sunnah to indicate that it is mustahabb to drink water or sips of water before eating food. Perhaps the one who thought that that is Sunnah imagined it because it is proven in the Sunnah that it is mustahabb to drink in three draughts. But this is something other than what the questioner thought, because the fact that that is mustahabb has nothing to do with eating food. It is the same whether one drinks before or after eating or whilst eating, or in any other situation; it is mustahabb for him to consume his drink in three draughts.
It was narrated that Anas ibn Maalik (may Allah be pleased with him) said: The Messenger of Allaah (blessings and peace of Allah be upon him) used to breathe three times when drinking, and he would say: “It is more thirst-quenching, healthier and more wholesome.” Narrated by Muslim in his Saheeh (2028).
Ibn al-Qayyim said: What is meant by breathing whilst drinking is moving the vessel away from the mouth and breathing outside of it, then going back to drinking. Zaad al-Ma’aad, 4/210.
There are great wisdom and important benefits in drinking in this manner. The Prophet (blessings and peace of Allah be upon him) drew attention to them when he said: “It is more thirst-quenching, healthier and more wholesome.”
Thirst-quenching means it is more hydrating and beneficial.
Healthier means it is better for one.
Wholesome means that it is healing; it relieves one from intense thirst and sickness to which that may lead, because it comes to the stomach in stages one after another; the second draught soothes that which could not be soothed by the first, and the third soothes that which could not be soothed by the second.
And it was said that wholesome means that it is free from any disease or harm that may result from drinking in one draught.
See: Sharh Saheeh Muslim by al-Nawawi, 13/199
Ibn al-Qayyim said: One of the problems caused by drinking in one draught is that there is a fear of choking, as the oesophagus may be blocked by the large amount of liquid flowing through it. But if he breathes slowly, then drinks, he will be safe from that. End quote.
Zad al-Ma’aad, 4/231
And Allah knows best.