Re: Anybody who knows anything about plumbing ...
Your mains water supply is a source. Your CH system isn't, it simply holds water that the source supplied. You're not coupling two sources together.
Once you store water, the water in that storage becomes a new "source". If I fill a barrel with water from the mains, then add a kg of potassium cyanide to that barrel, you are surely not saying that it is then OK to put that barrel on the top of a tall tower and plumb it into the mains water supply?