I've been full timing for 13 years and in all that time, never had a 'hard water' problem. Never replaced a tank, never had a faucet gummed up with deposits, never had a shower head clogged.
Probably because I am proactive with assessing the water hardness and mineral content of anywhere I stay. One of my first questions when I settle somewhere is about the water.
So with that in mind, what I do do is keep my tank nearly full while traveling with known good water. If I'm somewhere (and those places are few and far between) where I'm tipped off about the water being not good or very hard than I use the tank. Where there is good water, I fill the tank and use shore water.
Have an undersink water filter for drinking water, and a 2nd filter for the shore water faucet if it's problematic shore water.
But again, never have needed to change or fix anything because of hard water deposits over 13 years of traveling. Coast to coast, Mexico to Alaska. And many times I've stayed at parks where they have equipment to soften and purify the parks water!
I'm not totally against them, it's just the excess salt that comes from RV softeners is undesirable.