Softened water is any water that is un-distilled and then has salt (Sodium Chloride) and potassium added. Good for your laundry, not good for drinking.

Distilled water makes good coffee. But it should not be drank as a main water source due to the lack of minerals.

Tap water all depends on where its from and how its treated if at all. Well water may be full of good and bad.... Tap water from a Miniciple source can also be full of good and bad....

I have for the last 35+ years just added a 50/50 mix of distilled water and good ol GREEN stuff.

But with this 410 Stroker build I am installing an anode into the front and rear block drain plugs. There is enough room for a 0.90 inch long Zinc or Magnesium bar. I bought 5 of these for $20 and am just cutting them down to fit. The end I cut off can be threaded and used later so I really have 10 on hand. I will replace them every 2 years or so. See picture below

https://www.ebay.com/itm/Martyr-CME0-1-3-4-L-5-16-18-Thread-1-4-3-8-Dia-Plug-Engine-Pencil-Zinc-Anode/254316970289?hash=item3b36790131:g:~YAAAOSwZGFdQqeh

EDITED> The Ebay link for 5 pieces of these Anodes
https://www.ebay.com/itm/ZINC-ANODE-PENCIL-WITH-PLUG-70-E00C-SIZE-1-4-X2-PLUG-1-8-NPT-5-PACK-MARINE-BOAT/184015710240?hash=item2ad830e820:g:O6sAAOSwF1dUPrmk