Water… Distilled? Purified? Hose??

Distilled. its available in any decent supermarket.
50/50 with 'Conventional' anti-freeze.
I've learned my lessons the hard way. Much cheaper in the long run. Copper radiators and heater cores are expensive to repair and replace. Rusted out core plugs even more so.

By "conventional" it must have an inorganic anticorrosion additives including phosphate and silicates. Usually colored green, but beware some companies market a greenish "universal" that is a HOAT.
Propelyne glycol is not a solution to corrosion. It also needs corrsion inhibitors. (I invistigated this when we needed a highly efficient coolant for an industrial chip writing machine. ) That's true whether its the safer version sold in the general market, or the no-water version.