The said water is purified by means of either one of the processes like double distillation, reverse osmosis, deionization or more than one of them.
Step-by-step explanation:
In chemical analysis of a chemical substance, the water used is needed to be free from any sort of chemical ions that are generally present in tap water. These ions if present may interfere in the chemical reactions in which water is used as a solvent, or can interfere with the values of estimation of a particular ion.
So the water is either distilled for two times to get rid of any types of ions dissolved in it. Or it can be purified by means of reverse osmosis through a semipermiable membrane. Or it can be deionized by means of using electrolysis at particular voltages. More than one processes can be done to get higher percentages of purification.