A thermal water purification system and a related method including distilling units consecutively flowed through by raw feed liquid, each having a boiling liquid section and a vapor section, and including a heat exchanger cavity adapted to transfer thermal energy to the raw feed liquid before entering the boiling liquid section of a first distilling unit. Heat exchanger tubes in fluidic communication with the heat exchanger cavity extend through the boiling liquid section of the first distilling unit to transfer thermal energy from a medium in the tubes to cause the raw feed liquid to boil. Preheating tubes extend through the vapor section of each distilling unit to heat the raw feed liquid before entering the boiling sections using thermal energy from vapor condensing against external surfaces of the preheating tubes, which produces the distillate liquid that flows through a discharge port and a conduit supplying a storage tank.