**5. Remineralization**

Drinking water produced via reverse osmosis (RO), including that obtained from household systems, water vending machines, and almost all bottled waters, is sometimes remineralized in order to improve taste or nutrition, as well as to achieve specific goals for pH and ORP. Without the remineralization of alternative waters, TDS concentrations are typically less than 20 to 30 ppm. Whereas, the remineralization of low TDS waters is designed to address taste and potential deficiencies of major minerals, there are some interesting questions related to how and why the waters are remineralized.

Perhaps most controversial is whether routinely consuming low TDS water poses a risk to people by osmotically extracting minerals from the body's structures or extracellular fluids that possess higher mineral contents. Whereas mineral leaching has been identified for foods that are cooked or prepared in low TDS water, a similar leaching process has not been demonstrated in human bodies [22,23]. Healthy bodies possess an array of integrated control systems (e.g., sensory, hormonal, excretory) for retaining or expelling specific minerals to maintain the ionic composition of extracellular fluids.

Other questions about water remineralization relate to both the actual salts that are utilized and the ratio of major minerals in added solutions. The most common additives to low TDS waters are calcium carbonate and magnesium oxide, which have limited bioavailability but raise the pH and provide a buffering effect. Other sources of mineralization include various salts, concentrated mineral liquids, and even seawater, most of which are dominated by sodium and chloride. Though seawater has a mineral composition similar to that of blood plasma, it has an ORP higher than most natural freshwaters and often contains organic compounds derived from marine organisms. While some of these compounds have potential health benefits, their addition to alternative waters is unlikely to be implemented.

Some drinking water additives claim to have an ideal ratio of major minerals or a suite of important trace minerals. However, most trace minerals are provided by food and, although drinking waters may emulate the ratio of major minerals in extracellular fluids, there are numerous factors that can result in the differential absorption of those minerals. Consequently, minerals are not necessarily absorbed in proportion to the ratios reflected in liquids, salts, or other additives, requiring the body's homeostatic processes to maintain the precise suite and concentration of minerals comprising those fluids.

When remineralizing alternative waters with a low TDS, an important consideration is taste. Taste is a function of the minerals dissolved within it, as well as its temperature, oxygen content, pH, and organic carbon content. Palatability is also influenced by people's own taste sensitivity and by any materials or chemicals that contact the water during its treatment, storage, or transport [24]. Perhaps as important, from a nutritional perspective, is the presence of calcium and magnesium, the latter of which is a common mineral deficiency due to its relatively low concentration in most foods. The bioavailability of magnesium from mineralized waters is similar to that from foods, and its levels in bodily fluids are stringently controlled by the kidney's excretion and retention processes [25].
