Finding the figure
Your water supplier publishes hardness by postcode or commune, on their website and in the annual water quality report they are required to produce. That figure is for the supply you actually receive, which is better than any test strip.
Test strips are still useful for one thing: checking later that a softener is doing what it should.
The three units
°dH — German degrees, standard in Germany and Austria. °f — French degrees, used in France and Italy. mg/l or ppm of calcium carbonate — usual in English-language specifications.
They convert directly: 1 °dH is about 1.79 °f and about 17.8 mg/l. A specification quoting one and a supplier quoting another is the normal situation, not a problem.
What the number means
Below about 7 °dH the water is soft and scale is not a problem worth spending on. Above about 14 °dH it is hard, and it is the range where kettles fur, screens spot, aerators block and softeners get bought. In between, it depends on how much it annoys you.
What it changes when you buy
A softener, obviously — its capacity is a volume of water at a given hardness, so the same unit treats twice as much soft water as hard between regenerations.
A shower head, because in hard water a face with flexible cones you can rub clean is worth more than any number of spray modes.
A finish, because matt black and brushed surfaces display the white deposit that chrome hides — and because the acidic descaler that removes it is usually forbidden on them.
What the number does not mean
Nothing about drinking water quality, which is regulated separately and is a matter for your supplier. Hardness is a scale question, and this site keeps it as one.
Questions people actually ask
Does hardness change through the year?
It can, where a supplier blends sources seasonally, which is why published figures are often a range. Sizing against the harder end is the cautious choice.
Is a whole-house softener the only option?
It is the one that changes every outlet. Point-of-use scale filters exist for a single appliance or shower, and they address that one place. Which is appropriate depends on where the scale actually bothers you.
Last reviewed 5 September 2026
