Heat energy is required. In distillation, the solution is first heated, where heat energy is required, such as using a bunsen burner. When the solution is heated, the water may reach its boiling point and evaporate. However, salt does not. When water molecules evaporates, it travels through a condenser that cools it down into liquid again. Therefore we get pure water. Salt is also obtained in the original beaker. Therefore to first start this process, heat energy is required.
