Asalaamu alaikum sisters
So I went out and bought zamzam water for my son so he throughly understands inshaAllah about the story behind it. The zamzam well was revealed to Hajar (ra), the wife of Ibrahim (as) and mother of Ismail. Ibrahim (as) was commanded by Allah swt to leave them in the dessert, with only one skien of water, as a test. After a while, Hajar finished the water was desperately seeking more for her infant son, but could find none. Hajar ran seven times back and forth in the scorching heat between the two hills of safa and marwah, looking for water. *Upset and getting thirstier by the second, Ibrahim scraped his foot against the ground. Allah saw how desperate Hajar was so he sent angel jibreel down to make water come up out of the ground under her son’s feet and it turned into a well and since has never stopped flowing. Zamzam means exactly that, nonstop, and alhamdulillah, it has been running for thousands of years up to now.
*note: the version of this I had heard was that Allah saw how determined Hajar was and He sent the angel Jibreel to hit the rock and the water started flowing for Hajar, as sr.muneera mentioned in the comments below, although I was not able to find this online, though it is close. Another version also mentions that once Hajar was able to drink from the water, her breastmilk increased so she was able to feed Isma’il mashaAllah.