Soft Water for Drinking and Low Sodium Water Explained

Soft water has little dissolved calcium and magnesium. On the US Geological Survey’s scale, hardness up to 60 mg/l as calcium carbonate counts as soft. Low sodium is a separate question: under EU rules, a natural mineral water can say it is suitable for a low-sodium diet only if its sodium is below 20 mg/l.

What makes water soft or hard?

The USGS defines hardness simply as the amount of dissolved calcium and magnesium in the water. Its scale, expressed as milligrams per litre of calcium carbonate, calls 0 to 60 soft, 61 to 120 moderately hard, 121 to 180 hard, and anything above 180 very hard.

You will also see degrees of German hardness, °dH. One °dH is about 17.8 mg/l as calcium carbonate, so the USGS’s soft limit of 60 mg/l is a little over 3 °dH. Norwegian water companies tend to quote °dH. Oslo’s drinking water, for instance, is about 2.5 °dH, and the city says you don’t need dishwasher salt.

Where does FRØYA land on hardness?

The label doesn’t state a hardness figure, so here is our own calculation from the Eurofins report. The standard conversion is calcium × 2.5 plus magnesium × 4.1, giving the result in mg/l as calcium carbonate. FRØYA’s sample had calcium at 16 mg/l and magnesium at 1.1 mg/l, which works out at roughly 44 mg/l, or about 2.5 °dH. That is soft on the USGS scale.

It is also almost the same as Oslo’s tap water, which Oslo kommune reports at 1.9 to 2.8 °dH with calcium of roughly 13 to 20 mg/l. On hardness alone, you wouldn’t tell a FRØYA bottle from an Oslo tap. You can check the source figures on the analysis page, and keep in mind that the sample dates from March 2018.

How do you work out hardness from an analysis?

You don’t need a lab. Take the calcium figure, multiply by 2.5. Take the magnesium figure, multiply by 4.1. Add the two. The answer is hardness in mg/l as calcium carbonate, and you can compare it with the USGS bands. Divide by 17.8 for °dH.

Worked through with each brand’s own published figures, it looks like this. Voss’s Norwegian still water, with calcium 2.7 and magnesium 0.61, comes to roughly 9 mg/l, very soft. FRØYA, at 16 and 1.1, comes to about 44 mg/l, soft. Fiji, at 18 and 14 in its February 2025 report, comes to about 102 mg/l, moderately hard. Evian, at 80 and 26, comes to about 307 mg/l, which is very hard on the USGS scale. These are our calculations from published analyses, and the brands don’t state them. They also assume the figures are current, so treat the results as a rough guide.

Is soft water good to drink?

Soft water is common in Norway. Vestfold Vann, a regional water company, says Norwegian surface water sources usually contain little salt and the water is called soft, while groundwater tends to be harder. Hardness is mostly a household matter: scale in kettles, soap that lathers less. The Maryland Geological Survey says plainly that hard water does not pose a health hazard.

Going the other way, WHO notes that water with extremely low TDS can taste flat, and the USGS says extremely soft water is likely to corrode metals, which is a pipework issue rather than a drinking one. None of these sources treats soft drinking water as a health problem. So the honest answer is that it comes down to taste. We aren’t going to tell you soft water is healthier, because no source we cite says that.

Is softened tap water the same as naturally soft water?

No, and this catches people out. Home water softeners usually work by ion exchange, swapping calcium and magnesium for sodium, as the Maryland Geological Survey describes. A tap softened at home can end up with more sodium than a water that is soft by nature. If sodium matters to you, the source of the softness matters too.

What does low sodium mean on a bottle?

FRØYA’s sample had 4.8 mg/l of sodium, which the label calls natrium. WHO proposes no health-based guideline value for sodium in drinking water, because the contribution from drinking water to daily intake is small. It puts the average taste threshold at about 200 mg/l. At 4.8 mg/l, FRØYA is roughly forty times below that.

In EU rules, the wording on a label is regulated. Annex III of Directive 2009/54/EC lets a natural mineral water say “suitable for a low-sodium diet” if its sodium is below 20 mg/l, and “contains sodium” above 200 mg/l. That wording is for recognised natural mineral waters. The Eurofins report marks FRØYA as a spring water, so we are not making that claim. We are only telling you the number.

For comparison, the brands publish sodium of 3 mg/l for Voss’s Norwegian still water, 6.5 for Evian and 16 for Fiji. If a doctor has put you on a sodium restriction, ask them what applies to you, since WHO’s point is that water is rarely the main source.

How do you choose, then?

Look at the analysis rather than the adjective. Calcium and magnesium tell you about hardness, sodium about salt, and pH and TDS about taste and chemistry. Our guide to reading a bottled water analysis shows how, with FRØYA’s real numbers, and spring water vs mineral water explains which labels are legally defined.

Frequently asked questions

Is soft water safe to drink?

Yes. The sources we cite treat hardness as a household matter, such as scale and soap, and the Maryland Geological Survey says hard water does not pose a health hazard. Soft versus hard drinking water is mostly a question of taste.

Is FRØYA soft water?

By our calculation from the 2018 Eurofins report, yes: calcium 16 mg/l and magnesium 1.1 mg/l give about 44 mg/l hardness as calcium carbonate, or roughly 2.5 °dH. That is soft on the USGS scale.

How much sodium is in FRØYA water?

4.8 mg/l, listed as natrium on the label, in the March 2018 Eurofins sample. The measurement uncertainty for sodium in that report is 20%.

What counts as low sodium in water?

The EU allows natural mineral waters to say “suitable for a low-sodium diet” below 20 mg/l of sodium. FRØYA’s sample is marked as spring water, so the site makes no such claim.

Does softened tap water have more sodium?

Often, yes. Ion-exchange softeners replace calcium and magnesium with sodium, so a home-softened tap can contain more sodium than naturally soft water.

Sources

Figures for FRØYA come from Eurofins report AR-18-MO-004161-02 (sample taken 20 March 2018, report dated 11 April 2018), which covers one sample. Figures for other brands are taken from the pages linked above and may have changed since. This article is general information about water, not medical advice.

Soft Water for Drinking, and What “Low Sodium” Means on a Bottle