Actually , pure water is not heavily ionized, the correct description would be a very stable molecule.

Distilled water doesn't have the minerals (disolved salts including usually alot of calcium)but when it does then you have alot of ions disolved which are what cause the precipitous deposits you get in you cooling system. These same salts are responsible for helping transmit current and another form of creating deposits and that is electrolysis. Pure water doesn't conduct electricity.

To clean your cooling system, buy a couple of gallons of the cheapest vinegar you can find , drain the fluid and replace with the vinegar. Run the engine for 1/2 hour letting it come up to temp so the thermo is open and also keep the heater on so the core gets washed . The acetic acid in the vinegar will dislodge and dissolve most mineral deposits. Shut off engine , let cool till warm , drain , and flush , drain then flush with 1 Tablespoon baking soda/ gallon water , let sit for 1/2 hour then drain once more and flush till your hearts content.

Replace with your favorite coolant (i like toy-red) and distilled water only

Baking soda ,,, not baking powder!