You would think that cavemen didn't have the technology to know fresh water is underground. So they probably got their water source from open bodies of it. So why didn't we evolve to tolerate cholera and other parasites found in sitting water? Why does science get to control the narrative and ignore these simple facts? In fact, finding clean water would have been impossible in cavemen times, they all should have died. There is zero evidence that cavemen knew groundwater was cleaner than river or pond water.