You really don't want to be drinking heating system water even if there are no additives, as is usually the case in residential.

When it comes from the water supply provider it has disinfectants in it, either chlorine or chloramine, but those disappear quickly and the bugs begin to grow. Bacteria, slime, etc. Look at what comes out of a fire sprinkler system sometime, it's black and slimy. Water has a shelf life that is long exceeded in a heating system.

Tim:

I wouldn't want to drink hydronic water either. Even if I was thirsty.

But, your point that soft water is chlorinated, and that once the protection afforded by the chlorine is gone, the water will start to have bacteria growing in it needs to be addressed.

Bacteria, just like every other living thing, needs food to grow and multiply.

That is, the reason there aren't very many people living in the Sahara Desert is because there isn't enough food in that desert to support a large population.

And, I just don't know of anything inside a hot water heating system that would provide the food needed for bacteria to grow and multiply. And, there's lots of evidence to support the notion that there isn't any bacteria growing in boiler water:

Whenever I've taken a piece of threaded iron piping out of my hot water heating system, there was no slime anywhere to be found inside that piece of pipe. Ditto for my father's (now deceased) building which had a cast iron boiler and copper distribution lines.

Also, the place in a hydronic heating system where the water comes the closest to being stagnant (and therefore best suited for bacteria to grow) is in the float chamber of the Low Water Cut Off. Where I live, the low water cut off on commercial boilers has to be tested every year to ensure that it's working properly. Every time my boiler inspector has tested my heating boiler(s) low water cut off(s), lots of water came out of each one, but never any slime. So, I don't believe there's any slime in there.

Anyhow, I'm not suggesting people drink boiler water. All I'm doing is questioning the widely held belief that the stuff is unfit to drink. It's that questioning of widely held beliefs that leads to discovery, like the discovery of North America, for example. Contrary to popular belief at the time, it turned out that the Earth wasn't flat after all.