In the times of the Prophet Yirmiyahu (Jeremiah), natural springs provided water for the ancient Israelites. Some people also carved out cisterns in which to store the rain to ensure they would have enough to drink. Inevitably these man-made cisterns would crack and the water would be lost. Yirmiyahu compares Hashem to a fountain of natural spring water, while false gods are likened to cracked cisterns. Yirmiyahu’s message is to remember that Hashem is true source of  life and blessings and not to be confused by claims of false gods or idols.