According to :

The simple, and cost effective answer to your question is... get a
properly sized and setup industry standard softener from a water
treatment professional, soften the ENTIRE house, and set the softener
to use KCl (potassium chloride) as a regenerant.

What if you're on a sodium, or worse, potassium reduced diet? ;-)

Why on earth would you deliberately soften water to the exterior
hose bibs if you can avoid it?
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.