Praise be to Allaah.
The water of Zamzam is water of great virtue which first sprang forth when Jibreel (peace be upon him) struck (the earth) with his wing (Saheeh al-Bukhaari, 3364). Allaah provided water for Ismaa’eel (peace be upon him) and his mother with it. The heart of the Prophet (peace and blessings of Allaah be upon him) was washed with Zamzam water. Many saheeh ahaadeeth have been narrated concerning its virtues, such as:
The Prophet (peace and blessings of Allaah be upon him) said: “The best water on the face of the earth is the water of Zamzam; it is a kind of food and a healing from sickness.” (Saheeh al-Jaami’, 3302).
It was reported that the Prophet (peace and blessings of Allaah be upon him) drank it, did wudoo’ with it and poured it on his head. He used to carry Zamzam water in small vessels and large containers in order to pour it on the sick and give it to them to drink. (al-Silsilat al-Saheehah, 883).
One of the Sahaabah said: we used to call it al-Shabbaa’ah (satisfying) and it helped us to take care our families (i.e., it was filling and helped them to do without food, it was also sufficient to nourish children). (al-Silsilat al-Saheehah li’l-Albaani, 2685).
The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The water of Zamzam is for whatever it is drunk for.” (Narrated by Ibn Maajah, 3062; this is a hasan hadeeth. Scholars and righteous people have experienced this – they have drunk it with the intention of fulfilling some need such as healing from sickness or being freed from poverty and distress, and Allaah fulfilled these hopes).
And Allaah knows best.