Sodium in water is measured in milligrams per litre, and the spread across the shelf is enormous. In this catalog the lightest verified water carries 0.2 mg/L and the heaviest carries 3,350. That is a factor of sixteen thousand between two things both sold as drinking water, which is why the label is worth reading if salt matters to you.
Where the line falls
European labelling law is specific. A water may be described as suitable for a low sodium diet when it carries less than 20 mg/L, and as very low sodium under 2 mg/L. Those thresholds are the only ones with legal meaning, and most bottled water clears the first comfortably. Of the 389 waters here with a published analysis, 206 come in under 20 mg/L, so a low sodium water is the normal case rather than a specialist product.
The waters at the very bottom are mostly Alpine and Pyrenean. Acqua Dolomia carries 0.2 mg/L, San Bernardo 0.58, Courmayeur 0.7, Luchon 0.8. Among the widely stocked names Highland Spring sits at 5.6 and Evian at 6.5, both far inside the line. The sodium table ranks the whole catalog, and the low sodium collection gathers the ones worth drinking for pleasure as well as arithmetic.
The other end, and why it exists
Some waters carry startling amounts of salt on purpose. Vichy Célestins holds 1,172 mg/L of sodium, Saint-Yorre 1,708. These are sodium bicarbonate waters from volcanic France, drunk historically as digestives rather than as refreshment, and they taste frankly of it. They are not mistakes and they are not diluted seawater. They are simply a different category of thing, and a single glass of Saint-Yorre carries more sodium than most people expect from a whole day of drinking water.
Sparkling complicates the picture, because carbonation is often added as sodium bicarbonate and quietly lifts the figure. If you want the bubbles without the salt, the low sodium sparkling collection is the narrow set that manages both.
Who should actually care
For most people water is a rounding error in a daily sodium budget dominated by bread, cheese and anything from a packet. Two litres of a 6 mg/L water contributes 12 mg against a daily intake usually counted in thousands. It becomes worth attention when a doctor has asked for sodium restriction, when the water is being used for infant formula, where the thresholds are stricter and worth reading properly, or simply when you notice that a water tastes savory and want to know why. Sodium is usually the answer.
The quickest way through it is the quiz, which asks about salt directly and rules out anything above your line.