The Prophet (peace and blessings of Allah 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 Allah 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 of our families (ie. 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 Allah (peace and blessings of Allah be upon him) said: "The water of Zamzam is for whatever it is drunk for." (Narrated by Ibn Maajah)
The Messenger of Allah, salallahu alayhe wa sallam has said:" The most sublime of all earthly waters is that of zamzam; therein one finds food for the hungry and medicine for the ill." [ At- Tabarani ]
"Zamzam water is what one intends to drink it for. When one drinks it to be healed, Allah heals him; when one drinks it to be full, Allah makes him full; and when one drinks it to quench his thrist, Allah quenches it. " [ Ahmad, and Ibn Majah]
Since Zamzam water serves whatever purpose and intention for which it is drank; provided it is with sincerity: The scholars and the righteous have tried this and they drank from it with the intention of fulfilling their needs and seeking cure for the sick or relief from poverty or catastrophe and surely Allah eased for them achieving their needs. So next time when one gets the opportunity to drink Zamzam, one should grab the opportunity to pray for: a healthy body, sharp mind, forgiveness for sins, life in Jannah after death, an honourable death on the day of Jummah, and all one's physical and spiritual needs of this world and Hereafter.
Imam ibn al-Qayyim al-Jawziyyah, may Allah have mercy on him, said, "Zamzam water is the best and noblest of all waters, the highest in status, the dearest to people, the most precious and valuable to them. It was dug by Jibril and is the water with which Allah quenched the thirst of Isma'il."
It was reported in Sahih Muslim that the Prophet, sallallahu 'alayhi wa sallam, said to Abu Dharr, who had stayed near the Ka'bah and its coverings for forty days and nights with no food or drink other than (Zamzam), "How long have you been here?" Abu Dharr said, "I have been here for thirty days and nights." The Prophet, sallallahu 'alayhi wa sallam, said, "Who has been feeding you?" He said, "I have had nothing but Zamzam water, and I have gotten so fat that I have folds of fat on my stomach. I do not feel any of the tiredness or weakness of hunger and I have not become thin." The Prophet, sallallahu 'alayhi wa sallam, said, "Verily, it is blessed, it is food that nourishes."[Narrated by Imam Muslim, 2473]