If something is dissolved in water then it can be extracted by evaporating it and then condensing the vapour, leaving the solute behind.

Distillation is required if the water is mixed with another liquid.

Distillation involves separating liquids according to their boiling points.

If you heat a mixture of liquids to the boiling point of one of the liquids, you know the liquid coming off at that temperature is the one whose boiling point it is.

Eg: If you mix ethanol and and water and heat it to 78°C, then the vapour coming off must contain alcohol, as 78°C is the boiling point of ethanol.