Wow! Wow! DO NOT USE SOFT WATER! Only use distilled water..it's cheap and you can get it at any Walgreens, Rite Aid, grocery store, etc. I know Jay Ross of Applied Chemical Specialties and he is sharp guy and knows a lot of stuff...but in this case he is mistaken. Water softeners do add sodium chloride, BUT THAT'S SALT, as in salt water, which is super-duper corrosive to all engine metals. You do not want salt water in your cooling system.
To give Jay some credit, he is 1/2 right. If you used ONLY distilled water (no ions in it), it would indeed start to dissolve cooling system metal (aluminum, cast iron, brass, steel... all the metal "ions" dissolve into the water). That part is true, but we won't be using only distilled water.....by using one of those corrosion inhibitor/surfactant blends (Lucas, Royal Purple, Water Wetter, etc.) we are adding "ions" into our distilled water (so, it's not really pure distilled water & the corrosion Jay talks about doesn't happen) to make the water-only coolant. Distilled water is used in making the coolant to make absolutely, positively sure only the ions that protect metals get into the coolant (the corrosion inhibitors), an no others. Chloride & sulfate are probably the two worst ions to get in your coolant, so DEFINETLY do not put sodium chloride aka "salt" (from soft water) in your cooling system.
And speaking of salt..... DO NOT EVER use an antifreeze called "Super ***" which comes in a yellow bottle with a blue label, it is really cheap, is green and I see it most often at gas stations. It says something on the back like 'does not meet any automotive manufacturers specification' or something like that, so at least they're honest. That stuff is green salt water....no lie.