The question of whether purified water and demineralized water are the same arises from common confusion in water terminology. While both terms describe water with a high degree of cleanliness, they are not strictly interchangeable. Understanding the distinction requires focusing on the goal of the treatment process. This article will define these terms, examine the processes that create them, and clarify their relationship and implications for human consumption.
Defining Water Purification
Purified water is a regulatory classification, signifying that the water has been processed to remove chemical pollutants, microbes, and particulates to meet a specific, high-level standard of cleanliness. In the United States, criteria for purified bottled water often align with standards set by the U.S. Pharmacopeia (USP), designed for pharmaceutical and laboratory use. This standard requires the water to contain no more than 10 parts per million (ppm) of Total Dissolved Solids (TDS). TDS measures all organic and inorganic substances dissolved in the water. The classification is primarily concerned with health and safety, ensuring the removal of harmful contaminants like heavy metals, toxic chemicals, and bacteria.
Methods of Demineralization
Demineralization refers to the targeted process of removing inorganic salts and ions, which are the minerals dissolved in water. Several distinct scientific methods are employed to accomplish this high degree of mineral removal.
Distillation
Distillation is one of the oldest methods, involving boiling the water to create steam and then condensing the steam back into a liquid. This process leaves all non-volatile substances, such as minerals and salts, behind. Distillation is highly effective at removing minerals, bacteria, and other impurities.
Reverse Osmosis (RO)
Reverse Osmosis (RO) works by forcing water under pressure through a semi-permeable membrane with extremely fine pores. The membrane physically blocks dissolved inorganic solids, including mineral ions, from passing through. This process typically achieves 90% to 99% rejection of contaminants.
Deionization (DI)
Deionization (DI), also known as ion exchange, is a chemical process that uses synthetic resins to remove dissolved mineral salts. The water passes through two types of resin beds. Cation resins exchange positive mineral ions (like calcium and magnesium) for hydrogen ions (H+). Anion resins exchange negative ions (like chloride and sulfate) for hydroxide ions (OH-), effectively stripping nearly all ionic mineral content.
The Essential Relationship Between Purification and Demineralization
The terms are closely related because the processes required to achieve the standard of purified water inevitably result in water that is also highly demineralized. For water to reach the regulatory cleanliness required for purification, its Total Dissolved Solids (TDS) level must be reduced to near zero. Therefore, purified water is almost always demineralized water.
However, the reverse is not always true; not all demineralized water is purified. For instance, water treated only by deionization (DI) is extremely low in mineral ions, but the DI process alone does not effectively remove uncharged substances, such as bacteria or certain organic chemicals. Demineralization is the result of low mineral content, while purification is the standard of having a low concentration of all contaminants.
Health and Consumption Implications of Demineralized Water
The primary concern with the long-term consumption of highly demineralized water relates to the absence of essential minerals, particularly calcium and magnesium. These minerals are important for numerous bodily functions, including cardiovascular health and bone maintenance. Consistent consumption of water lacking these elements contributes to a lower intake of these nutrients.
Drinking water with extremely low Total Dissolved Solids (TDS) can also trigger physiological responses in the body. Consuming demineralized water can increase urine output, leading to a diuretic effect that may alter the body’s electrolyte balance. This can cause the body to excrete more sodium while retaining less potassium.
Flavor and Remineralization
Water with very low TDS often lacks the characteristic flavor provided by minerals, giving it a flat taste. For this reason, many commercial bottled waters that use demineralization methods like Reverse Osmosis are subsequently remineralized before bottling to improve the flavor and restore beneficial mineral content. Long-term, exclusive reliance on completely demineralized water is discouraged due to the lack of nutritional contribution.