Finding the Fountain of Youth was one of the early obsessions of Daniel's grandfather, Nicholas Ballard. He had traced the origins of the mythology to Chac, the Mayan god of rain, and claimed to have found evidence indicating that the source of the Fountain's youth-giving power was a piece of alien technology used by early Mayan tribes around 900 BC.
The Mayan god Chac was probably the Goa'uld Telchak, and the alien technology was probably the reanimation device of the Ancients, also known as Telchak's device, said to be hidden in a temple near a water source in Central America at a place where legend says all nearby water flows toward it. Although Ballard never found the device, he left behind extensive research notes which eventually led Daniel to a majestic waterfall in the jungle south of Tegucigalpa, Honduras, near a buried temple where he eventually discovered Telchak's device.
Cross Reference: Nicholas Ballard, Reanimation Device, Telchak
Episode Reference: Evolution