Purified water can come from any source, including spring water, well water, seawater, or municipal water. This source water is then processed by reverse osmosis or deionization to produce a water that is indistinguishable from distilled water from any other source. Purified water contains no dissolved solids. Purified water may also be unhealthy because minerals and ions are being pulled out of it due to reverse osmosis.
The human body needs ions for the brain to function properly. Many of these ions are attained through water, often under the name electrolytes. Distilled and purified water lack these ions, so prolonged ingestion of distilled or purified water may lead to brain malfunction.