I have questions regarding water ionizers.

First, do water ionizers filter, TOO? Or do you purchase them IN ADDITION to a filter? Or do you purchase one IN PLACE OF a filter?

I am considering purchasing a reverse osmosis system. Do water ionizers go with reverse osmisis filter systems? (I've heard them mentioned in the same breath so to speak in some information I've read in the past).

OR, are water ionizers their own thing, all by themselves? I need to have understanding about whether or not water ionizers do the filtering as well as alkanizing the water. Or if they're a separate purchase you need to buy after you have a good water filter?

Third, can you buy an under the sink kind, or are there whole-house ionizers only available? (they don't say where I've searched, tho they're quite expensive!)

Thank you.

Beth