Due to the incredibly hard water here in Southern California, I went a step farther than most.
First the water goes through a "grit filter" (a small screen filter that I reverse to blow out the crud after every use).
Then it goes through one of the medium canister resin filters to "pre clean" the water.
Then is goes through the largest of the CR Spotless rigs. The pre filter removes a lot of the crud in the water so the lifespan of the resin in the much larger CR canisters last over four times longer. And I found a source for the resin in bulk that got my refill cost down even farther. It's a cumbersome pain in the ass but otherwise I always seem to get water spots.
My "calculated cost" for clean water is down to about $2.80 a wash. Plus about a half hour of my time to haul everything out of the garage, set everything up, and put it away afterwards.
And I only use the filtered water for the soap buckets and the final rinse.
I'd love to move to a warm state that has nice soft water, but there aren't any
I am almost ready to invest in an industrial system that has separate tanks for the anion and cation mediums so that I could actually "re-energize" the resin media correctly with acids and bases and never (or nearly never) have to replace the resin media.