As with so many other things, Swedes seem to be happy to persist the myth of superior drinking and bathing water which actually doesn't match the facts, at all. The water in central Stockholm is a slimy cocktail of raw sewage, localized heavy metals from old industries, algae and pesticides.
These articles are unfortunately all in Swedish - swedes prefer to keep their bad news local:
Raw sewage from new apartment buildings connected directly to one of the most popular bathing places in central Stockholm that ran out freely for at least three years:
http://www.aftonbladet.se/nyheter/article12848092.ab
An article stating that the equivalent of 354 Olympic-sized swimming pools of raw sewage and polluted water gushes straight out into the middle of Stockholm's water every year:
http://gamla.mitti.se/bajsvattnet-rinner-ratt-ut/
An article about the large scale of health problems following outbreaks of serious bacterial infections from tap water infected by raw sewage systematically entering drinking water without ultraviolet cleaning:
http://www.dn.se/nyheter/sverige/manga-annu-sjuka-efter-para...
Large parts of Stockholm is (as many major cities are) old industrial land. The heavy metals and poisons eill unfortunately keep polluting for s long time still. Worse, the heavy metals don't count in most "water quality" measures, such as when grading water for swimming.
Still, the water in central Stockholm is much better than in many comparable cities. That doesn't mean it isn't bad compared to a non-major-city body of water, but it's very good by those standards. The standard "very good" here means fish and other wildlife is doing alright, and swimming is ok.
I think Swedish drinking water is usually excellent, although it's a lot worse in the major cities (where most people live).
That is a huge problem, and it doesn't have any nice solutions. Dumping it in a lake should be banned of course, but keeping it in gigantic on-ground piles of dirty snow is only slightly better as it will quickly ruin a huge part of parkland somewhere in the central city (can't drive it very far). Making a few large dumping grounds with groundwater protection would be great, but nimby+cost likely makes it difficult.
judging by this years' winter weather, global warming might solve this.
It is an El Nino year if I'm not mistaken, so the unusually warm Winter is expected in many areas.
Not to say I think climate change isn't a problem, but I don't think it's responsible for the current weather to the degree others seem to think. Although it would be nice to point to the current weather and say "living proof!", I think it's probably not correct.
These articles are unfortunately all in Swedish - swedes prefer to keep their bad news local:
Raw sewage from new apartment buildings connected directly to one of the most popular bathing places in central Stockholm that ran out freely for at least three years: http://www.aftonbladet.se/nyheter/article12848092.ab
Farm organizations warning about swimming in Stockholm's water after rainfall: http://www.lantbruk.com/debatt/varfor-ska-jordbruket-sta-vid...
Raw sewage that has run directly out into bathing water in central Stockholm from an apartment house for the past 85 years: http://www.dn.se/sthlm/sa-mycket-bajsvatten-rinner-ut-i-stoc...
An article stating that the equivalent of 354 Olympic-sized swimming pools of raw sewage and polluted water gushes straight out into the middle of Stockholm's water every year: http://gamla.mitti.se/bajsvattnet-rinner-ratt-ut/
An article about the large scale of health problems following outbreaks of serious bacterial infections from tap water infected by raw sewage systematically entering drinking water without ultraviolet cleaning: http://www.dn.se/nyheter/sverige/manga-annu-sjuka-efter-para...
Heavy metals and other poisons in Stockholm's water: http://www.aftonbladet.se/nyheter/article10358091.ab