Calcium and magnesium are only healthy. There's pretty hard water in most of Sweden too. Ridiculous.
Salts, silly.
Do you understand what salts are? Neutralised/combined positive and negative elemental ions? I am not talking about carbon-bearing forms of those elements in compound, which we generally need in high quantities to survive. We call that food. If we could metabolise these types of salts, there would be no need to farm the planet or hunt for meat. We could just eat the soil. These salts of various ions are a hazard to health in the concentrations presented in many local water supplies.
Mine is one where they have difficulty keeping the concentrations below the national specification without the addition of several other harmful chemicals. In theory, the harmful chemicals (which are intended to create combined colloidal compounds from the near saturation level of salts and then are filtered or settle out to be dredged up and hauled away later) are actually being ingested, due to the high demand for water in most cities and the city's inability to keep up with the demand. People are drinking and cooking with water that has, not only a hazardous level of certain salts, but has had additional coagulating chemicals introduced, but too little time passes before the water is needed by the public. So the action expected of the coagulating chemicals has not occurred, yet. It will still occur, chemically, but it happens inside our bodies!
All you have to do to prove the presence of these chemicals in your tap water supply, is to make some ice and allow it to melt in a clear glass. If there are coagulating solid-like (often white-ish) speckles settling on the bottom, then your water has some bad shit in it. Don't drink it!
Read up, some. Go back and study biochemistry for a bit, then we'll talk.
I studied chemistry in high school, jerk. And your definition of salts is - of course - wrong. There are ions in many molecules that aren't salt molecules. A salt is a derivate of an acid; usually, but not always, a chemical compound of an acid and a metal.
I never heard of water being poisonous from calcium or magnesium salts. "Natural" calcium and magnesium salts are usually just healthy. When water is declared undrinkable in Europe, it's usually either because there are dangerous amounts of bacteria in it or chemicals from farming or industries. In Sweden the water is usually drinkable as it is from wells and even lakes and rivers; they just add a very small amount of chlorine in it to kill bacteria.
Interesting, really (and we are all very impressed - I mean we really are!), but the only difference in what you psoted (yeah, that's what you do, isn't it?) and what I posted is that you chose to make a point of the "mechanical" process which creates various salts, while I chose to point out the relevant point, supporting my use of the term "toxic" (the usage of which obviously was meant to be incendiary) as it applies to BIO-chemistry.
Did you notice that I did NOT mention hydrogen potential, as you did. It is hardly part of the danger, since most of those carbon-bearing, ion-rich compounds we eat can present from both sides of the hydrogen potential scale and hardly present a problem. What I was trying to express, is that the salts which cause problems are "ELECTRICALLY" neutral. Let's find out what that means to a biological process, then move one, please.
Electrical (positive/negative) neutrality in a molecule implies that the molecules are NOT repelled or attracted to each other in a powerful way. They can "float right next to each other" in the fullness of any biological process. However, the fact that these particular types of salt molecules are neutral in potential of "electrical charge" means that (since they are, as I stated, made up of neutralised combinations of opposing ions) they also sport a bipolar (duality) "mechanical" configuration and, when the geometry is just right, these molecules will attract end to end - remember they are bipolar. They will make little chains/groups where one negative pole attracts another (neutralised, electrically, which allows them to be "close together" (remember?) as the bio process continues) positive pole. It is this property that becomes dangerous to us if the concentration of these salts is high in our bodies. Little chains of neutralised ions create BIG groups of (OK, some metals if you must) non-metabolizible salts. This is where kidney stones come from, DUH!!
I am saddened that I had to spell this out so elementarily for you to understand why I supply my cat with purified water, but you DID seem to need more information to grasp why my cat is special.