Fresh water contains objects that must be removed to make it potable. These include large objects such as branches and leaves, insoluble particles such as grit, and harmful microorganisms. Different separation methods and treatments are used to deal with them:
Seawater contains too much dissolved salt to make it suitable as drinking water. However, pure water can be produced from seawater by simple distillation.
It is expensive to produce drinking water this way because large amounts of energy are needed to heat the seawater. However, water produced by distillation is useful in the laboratory for dissolving substances. It does not contain any dissolved ions that might interfere with a chemical analysis.