TDS · total dissolved solids
Every mineral in the water, summed in mg/L. Labels often call it dry residue, because the classic measurement is exactly that. Evaporate a litre and weigh what is left. TDS is the loudness knob. Under 50 mg/L a water is barely there; over 1,500 mg/L it is intensely mineral. It tells you how much is in the glass, not which minerals, so two waters with identical TDS can taste completely different.
The water world draws its low/medium line at 250 mg/L, and that is where our "light" and "full body" split lives too.
Carbonation · natural vs added
Carbonation is dissolved CO₂, and still versus sparkling is the fork you notice first. Natural means the gas rises with the water from volcanic or deep geologic ground; added means it is injected at bottling. The difference is provenance, terroir if you like, since the gas itself tastes much the same either way.
CO₂ also turns the water slightly acidic, which is where sparkling water's faint tang comes from.
Cation character · crisp vs savory
The dominant positive ion sets a water's temperament. Calcium and magnesium, the hardness minerals dissolved out of limestone, read crisp, chalky, clean-edged. Sodium, typical of volcanic and thermal springs, reads soft, silky, faintly saline.
Dominance is counted the way hydrochemists count it, by electrical charge rather than raw milligrams, which is why a water can hold plenty of sodium and still be calcium-dominant.
Anion character · round vs dry
The dominant negative ion shapes the finish. Bicarbonate rounds and soothes; it is what the classic digestive dinner waters are built on. Sulfate, dissolved out of gypsum, reads dry and faintly bitter, close to a brut wine's finish, and in quantity it is mildly laxative.
Most spring waters are bicarbonate-dominant; genuinely sulfate-dominant bottles are the rarer, drier shelf.
Magnesium · the tonic edge
Magnesium is the classic spa and recovery mineral, and in the glass it adds a bracing, slightly bitter edge. You only begin to taste it around 100 mg/L, and that is a sensitive palate; per Health Canada's review, most people need several times more. That is where our bitter-edge line sits.
The EU lets any label above 50 mg/L say it contains magnesium. That is a claim, not a flavor. Waters between 50 and 100 mg/L carry the words and taste of nothing much.
Silica · the beauty mineral
Silica dissolves out of volcanic rock and is marketed for skin, hair and connective tissue; it is the whole Fiji and Volvic pitch. It has little proven effect on taste, and a standard TDS meter cannot even see it, so it hides in plain sight.
It is also the least-published mineral on labels. When a producer gives no number, we say "not published" rather than estimate one. A missing value is information too.
Sodium · the 20 mg/L line
Sodium is the salt in your water. Most bottled waters carry very little, though thermal and soda springs can run 200–1,200 mg/L. If you watch your salt, the line to remember is 20 mg/L. Below that, EU law allows the claim "suitable for a low-sodium diet".
Low down, sodium is near-invisible to taste; it only turns savory much higher up. Choosing a low-sodium water costs nothing in flavor.
Virginality · how untouched the source is
How untouched a source is, read through its nitrate. Farming and settlement push nitrate up, and a deep, well-protected aquifer shows almost none, so under 1 mg/L is considered superior.
We report the published nitrate value for every water. It never affects your match, but it is one of the most honest single numbers about how isolated a spring really is.