Purified water, which uses processes such as dimineralization to remove impurities from natural water sources is defined and regulated by the Food and Drug Administration and the Environmental Protection Agency. As with most water sources--from bottled to artesian, purified water contains 0 calories. Nutritional value for all drinking water varies depending on how each water source is collected and treated.
Purified water contains four subcategories depending on the process used including: distilled, demineralized, deionized and reverse-osmosis water. According to federal regulations, purified water must contain no more than 10 parts per million of dissolved solids. If treated by reverse osmosis or distillation, purified water may also be free of microbes.