in the name of allah, most gracious, most merciful.
all praise and thanks are due to allah, and peace and blessings be upon his messenger.
anyone who is performing hajj is encouraged to drink water from the well of zamzam after completing the seven rounds of tawaf and offering two rak`ahs by the station of ibrahim. while drinking zamzam water, the pilgrim or the person who is performing `umrah is encouraged to make du`aa' for whatever he wishes in this worldly life and the hereafter.
in his response to your question, sheikh ahmad kutty, a senior lecturer and islamic scholar at the islamic institute of toronto, ontario, canada, states:
zamzam water is the most blessed water; it is a miracle of allah the almighty, and his chosen gift to his prophet isma`il and his mother hajar and through them to all posterity. the prophet (peace and blessings be upon him) is reported to have said, “it is a most blessed (water), good nourishment, as well as a source of healing for ailments.” he also said, “it can be drunk for whatever good purpose one has in mind. if you were to drink it for healing, allah will cure your sickness through it; if you were to drink it hoping thereby to seek allah’s protection, allah will protect you….”
inspired by such traditions of the prophet (peace and blessings be upon him), the early muslims used to offer various supplications while drinking zamzam water; one of the most comprehensive and yet concise of such du`aa's is the following; it has been attributed to the prophet’s companion, ibn `abbas (may allah be pleased with him):
(allaahumma innee as’aluka `ilman naïf`an wa `amalan mutaqabbalan wa rizqan wasi`an wa shifa’an min kulli da’in)
o allah, i ask of you to grant me beneficial knowledge, acceptable deeds, abundant provision, and healing/cure from all ailments.
may allah inspire us all to continually turn to him in supplications with true feelings of reverence, and in fear and hope. ameen