How many people visit the ka'ba each year?

Uncountable. Because only during Hajj season there are around 3 million Muslims from all over the world. After Hajj is over, Omra seaons on at all times and people keep visiting it everyday and night. If you go there at 3:00 am, you would still find it crowded. Water needs for this emormous amount of Guests of God are met by Holy ZAMZAM water, that's coming out of the earth and its source can not be found. Its been flowing since the time when Abraham left his wife Hagar and his son Ismael near Kaaba.