Where I live, the drinking water had won awards for how great it was. Sadly, all those things in the water aren't that great for our fish and other livestock.
What makes ro/di water such a necessity is that it is stripping everything out of the water. There are hundreds of things that we can't even test for, like fluoride, that isn't great for fish. These levels can rise and go unchecked and even cause total system failures. The things that we aim not to have in our systems, nitrate, phosphate, are also included in what is removed. By making the water stripped of everything in it, we can then control what is going into our systems with our salt mixes and anything else we decide to add to the system (like dosing).
