"Undrinkably foul" seems a bit melodramatic. It certainly has that distinctive minerally taste common to groundwater, which is quite noticeable to someone like me (and maybe you?) who lives in a city with chemically treated surface water. But in Europe using untreated or minimally treated groundwater seems to be a common approach and Copenhagen's was amongst the most neutral tasting to me. Iceland for example has much stronger tasting tap water.

This exactly. Just came back from Japan && New Zealand to Lithuania. I always thought we had great water, but now it tasted slightly foul (although very soft). I doubt that it gotten worse as we do a lot improve it.

Also, will never forget water in Switzerland (namely - Chur). Perfect, crisp, cold mountain water. Yumm. The worst water was in American Samoa, smelled like feces.

I don't think it has much to do with chemical treatment or not. A lot of U.S. cities also have hard water; that depends mostly on the source, with groundwater sources having more minerals than reservoir or lake sources. The main differences in U.S. treatment are that it fluoridates and chlorinates the water, it doesn't normally do demineralization. Also the fluoridation isn't even really a difference in this case: Copenhagen's water supply naturally has high levels of fluoride, similar to the levels that the U.S. adds.

But I agree Copenhagen's water is fine for drinking. I even like the taste. What it's a problem for is fixtures and appliances, which chalk up extremely fast, even compared to other areas I've lived with hard water. Showers, faucets, etc. all needs to be "de-kalked" at least every week, ideally every few days. Even simply leaving a glass of water out on the counter for one day will start to produce chalk lines that take effort to remove. Keeping an espresso machine operational is also a challenge, requiring pretty religious usage of the cleaning cycle with a de-chalking tablet.

Have you considered using bottled water with the optimum level of minerals for your espresso machine?

You kid, but it gets really frustrating when consumer goods die after two months because your tap water is pretty much liquid chalk. Pour a glass, leave it for an hour, there'll be a few mm of calcium carbonate precipitated out in the bottom of your glass. Can't use it for ice (just crumbles - too mineralised), coffee and tea end up with a skin, anything that quick-boils water, like an espresso machine, is destined for the trash heap.

I was being dead serious. A good espresso machine is a big investment and I think it's common for people to use bottled water in them when the local tap isn't ideal for taste or machine health.

I can imagine that kind of tap water being extremely frustrating. I've been very satisfied with the tap water everywhere I've lived, but it sounds like I'd be a bottled water guy in Copenhagen.

Optimal measures of bottled/mineral water for a coffee device? Is this reality that is worth getting out of bed for?

I would totally agree about the melodramatic. Try some water in parts of southern England. Would you like some water with your chlorine sir?

Yeah, the waters meant to be a lot harder down south. In the north west, you can taste the difference between filtered water and tap water but I happily drink tap water all day long.