The practical answer
Under 21 CFR 165.110, mineral water is a named type of bottled water with at least 250 ppm total dissolved solids from a protected underground source, and no minerals may be added to it. Bottled water itself carries no added ingredients apart from optional antimicrobial agents and fluoride within set limits. A water with added magnesium is therefore a formulated beverage that uses water as an ingredient, with its own name, ingredient statement, nutrition label and fortification rationale. [1–3]
What the bottled water standard allows
The US standard of identity describes bottled water as water intended for human consumption, sealed in bottles or other containers with no added ingredients, except that it may contain safe and suitable antimicrobial agents and fluoride within the limits in the same section. The standard also states that bottled water may be used as an ingredient in beverages, giving diluted juices and flavored bottled waters as examples. Processing and bottling must comply with 21 CFR part 129. [1]
For a magnesium fortified water formulation, this means the bottled water can be the base, but the finished product with added magnesium is not simply bottled water. Its statement of identity, ingredient list and nutrition label have to describe a beverage with an added mineral source. [1][4]
Mineral water is defined by its source
21 CFR 165.110(a)(2)(iii) defines mineral water as water containing not less than 250 ppm total dissolved solids, coming from one or more bore holes or springs in a geologically and physically protected underground source. It must show a constant level and relative proportion of minerals and trace elements at the point of emergence, allowing for natural fluctuation. No minerals may be added. [1]
Paragraph (a)(3)(i) of the same section requires the statement low mineral content on the principal display panel when the TDS of mineral water is below 500 ppm, and high mineral content when it is greater than 1,500 ppm; between 500 and 1,500 ppm no additional statement is needed. These figures describe total dissolved solids, not magnesium. Two mineral waters with similar TDS can carry very different amounts of magnesium, so a brief that says mineral water has not yet stated a magnesium target. [1]
Fortified water is a formulated beverage
In a fortified water the minerals come from specified ingredients added at a chosen level. The formulation team decides the elemental magnesium target, the source ingredient, the amount, the pH and the process. The ingredient statement follows 21 CFR 101.4, and magnesium on a Nutrition Facts panel is declared as elemental magnesium under 21 CFR 101.9, not as the weight of the source compound. [4][5]
Mineral fortification of beverages that are conventional foods also falls under FDA's fortification policy in 21 CFR 104.20, which sets out principles for the rational addition of nutrients and says FDA does not encourage indiscriminate addition. The 2015 FDA guidance adds that fortifying carbonated beverages, sweetened or unsweetened, is not considered appropriate under the policy. A sparkling fortified water therefore needs an explicit regulatory review, not only a stability test. [2][3]
Account for the magnesium already in the base water
Purified water may contribute little magnesium, while spring or municipal water can contribute a measurable and variable amount. Measure the base water with an appropriate elemental method, such as an ICP-AES method designed for metals in water, and repeat the measurement when the water source or treatment changes. [6]
Then calculate the added amount. If the base water contains 10 mg/L magnesium, a 500 mL bottle starts with 5 mg. To reach a total of 84 mg per bottle, the added ingredient has to supply 79 mg. At an as-is assay of 8%, that is about 0.99 g of ingredient per bottle. These numbers are an arithmetic example, not a recommended serving level. Total all sources before evaluating the label, and confirm the finished product by analysis. The beverage magnesium serving calculator does this conversion for a stated serving volume.
What to brief before the first bench trial
Record the base water type and specification, its measured magnesium and TDS, the elemental magnesium target per serving, the candidate ingredient and lot assay, the pH target, the decision on carbonation, the intended process and the package. Add an appearance target and a sensory reference, usually the same base water without added magnesium.
Natural mineral water and fortified water can both be good products. They are documented differently: one by characterizing a source, the other by specifying an ingredient addition. Keeping those two records separate avoids label errors and makes supplier discussions faster. How the distinction developed is in how magnesium entered beverage formulation from mineral water to fortified drinks.
Common questions
Can a water with added magnesium be called mineral water?
Not under the US standard of identity. 21 CFR 165.110 states that no minerals may be added to mineral water.
Does 250 ppm TDS mean 250 mg of magnesium per liter?
No. TDS covers all dissolved solids. The magnesium share depends on the specific water and has to be measured.
Sources & further reading
- 21 CFR 165.110, Bottled water
- 21 CFR 104.20, Nutritional quality guidelines: statement of purpose (fortification policy)
- FDA, Questions and Answers on FDA's Fortification Policy (November 2015)
- 21 CFR 101.4, Food; designation of ingredients
- 21 CFR 101.9, Nutrition labeling of food
- US EPA, Method 200.7: metals and trace elements in water by ICP-AES
