filtering systems are only effective against solids, and if they have activated charcoal (brita) the remove organics/hydrocarbons and SOME other compounds too.
RO and distillation systems remove minerals and ions.
Water softeners only exchange minerals with salt ions.
Um what am I forgetting?
Oh. UV sterilizes the water, removing bacterial and fungal pathogens, and I believe all/most viruses too, but leaving salt and mineral content unchanged.

What was the dose on that molasses?