They have individual counter-top models.
Under the sink models.
Whole house systems.
Check out Lowes or Home Depot before you cop from a hydro store.
Hydro spots tend to go crazy on their price markups, compared to our 2 largest home improvement corps.
Check and make sure the R/O system has ACTIVATED Carbon filtration.
That is the only way to remove Chloramine from your tap, which most major cities use now.
Chloramine = Chlorine + Ammonia molecules.
Has a longer shelf-life and therefore more effective at killing/controlling bacteria/fungi colonization at the treatment plants.
Problem is, due to that Ammonia molecule you can't sit a bucket out in the open (even w/ air stones bubbling) expecting it to dissipate (evaporate) like Chlorine.
It's amazing the number of ppl that THINK their city still uses Chlorine.
A simple call to your local water company will get you the answer about what they use to treat the water supply.