TDS stands for total dissolved solids. Boil a litre of water away and weigh what stays in the pan, and that is the figure, written in milligrams per litre. Everything counts toward it, the calcium and magnesium, the sodium, the bicarbonate and sulfate and chloride, the trace of silica. It is the whole mineral load reported as one weight, which is why it is the fastest way to know what a water will feel like before you drink it.
What the number tastes like
A water under about 50 mg/L is barely there. San Bernardo sits at 34.9 and reads as almost nothing, clean and quick and gone. Between roughly 100 and 500 the water starts to have a body you can notice. Volvic at 109, Highland Spring at 160, Fiji at 230, Evian at 357. Above 1,000 the mineral stops being background and becomes the point. Gerolsteiner carries 2,500 and tastes unmistakably of the Eifel it came through.
Past that the numbers stop describing refreshment and start describing medicine. Borjomi runs to 3,900 and Donat Mg to 13,197, which is why it is sold by the small glass rather than the bottle. The full TDS table lays the whole catalog out from lightest to heaviest.
Why a high number is not a better water
This is the part the number is most often used to get wrong. TDS is a weight, not a verdict. It cannot tell you whether the minerals in the water are ones you wanted, because a litre carrying 500 mg of bicarbonate and calcium and a litre carrying 500 mg of sodium chloride report the identical figure and taste nothing alike. A cheap meter that reads TDS at the tap tells you the same thing, and shop assistants sometimes present a low reading as purity. It is not. Distilled water reads close to zero and tastes of nothing, and some of the finest waters in Europe read high because they spent a long time in good rock.
What TDS is genuinely good for is placing a water on a scale before you commit to it, and comparing like with like. For everything the single figure hides you need the panel underneath it, the calcium, the magnesium, the sodium. Those are the numbers that decide the taste.
Where the figure comes from
On a European label the same measurement often appears as dry residue at 180 degrees, which is the laboratory method behind it, and the two are used interchangeably. Every water in this catalog carries the figure from its own published analysis, either the producer laboratory or an official register, never an estimate. Where a water publishes no analysis we say so rather than guess. That is also why purified waters like Dasani and Smartwater are hard to pin down, since their mineral content is added rather than drawn from a source and can move between production runs.
If you would rather not read tables, the quiz asks how much you want to taste the water and answers with a bottle at the right weight.