Why is it, then, that you want to process further? Does it taste bad, for example? Are you suspicious of other stuff that may be in it? What's your motivation?

Not trying to give you grief. Just wondering what your purpose may be. They are expensive and do require maintenance. Don't yet know why you want to do this.

I know nothing about the water supply in your area. These are innocent questions.

Be advised that pretty much all RO systems work exactly the same way. No variation in principal, only in product -- the actual product quality being very difficult for the average consumer to evaluate.

Basically pre-filter/membrane/storage-tank/post-filter. If you need more than that, there must be additional reason.

There have been a LOT of posts here about RO. Suggest using search function to find what's come before. Three really is a lot available. And by some very competent/experienced people.

You didn't say whether or not your "local water store" was previously known and/or trusted by you. And you didn't say whether you, yourself, are comfortable with DIY project like this or what your competence level may be....or not you want to do it or have someone else do it.