No, I don’t mean the citrus fruit you’d juice for a marinade (or a margarita) or squeeze into a Mexican beer. I’m referring to the cloudy limescale that builds up from hard water — and is a fact of life for most Danish residents.
When we moved to Copenhagen in 2016, I was shocked by the film left on bathroom tiles and otherwise shiny faucets (yes, I became a religious shower squeegee-er). Although I did appreciate the novelty of tap water with a slight minerality. Known as kalk in Danish (and in German, which was helpful when we relocated to Switzerland), limescale is commonplace for areas with hard water, although it was unfamiliar to me when we first moved to Europe. Having spent most of my life in the soft water environment of Vancouver, Canada, I had never thought about mineral deposits in water or the residue that gets left behind.
Soft water generally comes from areas with calcium-poor ground and rocks, while hard water comes from mineral-rich areas. Across Europe, most publicly supplied water is hard. Soft water doesn’t allow soap to generate tons of bubbles or provide easy-to-drink essential dietary minerals, nor does it leave chalky remnants in kettles or on faucets (or, even worse, coat hair and skin). Hard water can lead to dry skin and hair, cause mineral build-up in appliances and on fixtures (anyone else get annoyed with clogged showerhead nozzles?), and leave white spots or cloudiness on glass.
Of the three regions I’ve lived in with hard water (those would be Copenhagen, Zurich, and south of London in the UK), the Danish capital takes the crown. Water hardness in Denmark’s most densely populated region ranges from around 15 dH (degrees of hardness, see below for an explanation of what that means) up to over 25 dH. In case you’re curious, Zurich’s water is about 9.3 dH, with the water where we lived in England measuring about the same. The Vancouver suburb where I grew up comes in around 0.03 dH (yes, the water is that soft, no wonder we used a whisk to whip up foam for bubble baths).
In Europe, water hardness is commonly measured in degrees of Hardness (dH), a standard scale quantifying dissolved minerals. The Geological Survey of Denmark and Greenland (GEUS) gives seven categories of drinking water hardness:
- Under 4 dH = very soft
- 4-8 dH = soft
- 8-12 dH = medium
- 12-18 dH = fairly hard
- 18-24 dH = hard
- 24-30 dH = very hard
- Over 30 dH = extremely hard
For GEUS (and thus, for Denmark), proper ‘hard’ water starts at 18 dH — a massive difference from many other European countries, where 6.75 dH is viewed as ‘hard’, with water above 10.12 dH categorized as ‘very hard’.
Most of eastern Denmark (including the islands of Sjælland, Møn, Bornholm, and Fyn, as well as the areas around Horsens and Aarhus) has at least fairly hard water. I spent longer than I’d like to admit examining the GUES color-coded map displaying water hardness across the country. I can’t imagine how much limescale builds up in those dark blue regions!
Photo credit: GUES data.geus.dk
When we moved back to Denmark in 2025 after six years away, the municipality we decided to call home had harder water compared to where we lived during our first stint (from 15 dH to 19.6 dH). The difference is noticeable. We now towel off wine glasses rather than letting them air-dry on the dish rack, regularly descale drinking glasses, and have introduced a tap wipe-down into our post-shower squeegee routine. We’ve switched to using filtered water for the kettle and iron, which means descaling every couple of months instead of nearly every fortnight.
Twice a year, we pop limescale-busting tablets into both the washing machine and the dishwasher. White vinegar’s role in our lives has transformed from a fish-and-chips condiment to a cleaning solution (pro tip: dilute with water and pour into a spray bottle; let the solution sit for several minutes before wiping to deal with limescale as stubborn as the Danish insistence on proper rye bread). Our proactive efforts aren’t always successful, though. I had to laugh when my partner proudly showed off what looked like a fang, but was actually a limescale deposit he’d pried off the bathroom tap.
Our Swiss neighbors introduced us to Zitronensäure (citric acid or citronsyre in Danish), which dissolves calcium carbonate beautifully. Returning to the normal Copenhagener battle against limescale accumulation, we’re pleased citronsyre is readily available at grocery and drug stores (often in powdered form) — and we save the freshly squeezed lime juice for non-cleaning applications. (Definitely do not ingest citronsyre! Stick with salt rims for your margaritas!)
