We are on a well in Florida (FL has terrible ground water) and we use a 3-stage water conditioner - filter media for sediment and debris, filter media for positively charged contaminants, and filter media for negatively charged contaminants. When it was installed, we were told it was the same unit they use at Dunkin Donuts. Our drinking water is wonderful, and I just had to replace my water heater after 31 years - not because it wasn't clean and working well (it was, in both respects), but because our new house insurance policy wouldn't cover us unless the unit was less than 15 years old.
Our water conditioner has a single large pressure tank that contains all the filter media and has an electro- mechanical valve on top, and a side tank that looks like a plastic barrel that holds water softener salt. With 3 of us in the house it uses 40-60 lbs of salt per month but will hold enough for 3+ months if I let it go. Salt here runs around $9 for a 40-lb bag.
To answer the most basic question, the salt is not for treating the water. There is no salt in our household water. The filter media treats the water and the salt is used to clean the filter media. We have it set to regenerate every 3 days between 2-4am and no matter how much water we use, we've never exceeded the unit's capacity.
I am so hooked on having a water conditioner, I would have one even if we had city water.