Mecca was located in a dry  dusty depression in the Arabian desert.  Taif, nearby, was much more comfortable and had much better water.  Allah, a god of little concern for the faithful, even made sure Mecca had some of the most wretched water in the area.  The well Zamzam is undrinkable unless the Muslim drinking it just wants to get a spiritual rush.  Otherwise, it is a curse on the city of Mecca.