If the water was already hot because I was doing something else, I'll make soup or pasta with a pot of hot water. If the kitchen were closer to my water heater, I'd do it more consistently.
You're never supposed to cook with hot tap water. Even if lead is not a concern, there are other possible contaminants that can leech from plastic and copper pipes, or from the tank itself.
There's a lot that's not formally taught in the US. But I'm in the US and this is a thing. The blended faucets are fine. If it was set to hot or some blend with hot in it, you set it to cold and let it run for 1-3 seconds.
Seems like the presence of the accumulated gunk in the cylinder means the hot water must be cleaner by definition? The accumulation being the net difference between what was dissolved in the incoming water and what is dissolved in the outgoing water.
With the exception of gunk that is from the lining of the cylinder itself of course.
There can't be more minerals coming out than what went in though. It's not like calcium grows. Maybe it might break off and come out as some concentrated chunks, but overall there would have to be less coming out for it to accumulate in the tank.
For things like an instapot where you add a cup of water to it, you are actually supposed to use distilled water. I used tap for years with mine and got all sorts of mineralization. It took quite a bit of vinegar to get that off, and now everything looks pristine since I have been using distilled water. You might consider using it for your next kettle, although perhaps the minerals in tap do something to the taste of the tea.
