Freezing is one way to desalinate salt water. When salt water freezes, the salt is left out of the ice crystals as they form. Once frozen, the salt remains on the outside of the ice and can be brushed away before melting.
Other methods to desalinate salt water include evaporation and reverse osmosis. Salt can be removed by boiling water and capturing the steam vapors. This process is called distillation.
The method of reverse osmosis is the only man-made process. It includes pumps and a filtering membrane. The process forces the salt water through the membrane, separating the salt from the fresh water.