Ro Unit, Please Help, Thanks

[1Filmproducer]

Im thinking of getting discus fish to breed but i have hard water in my location. SO i was advised to get a ro unit, but how do they work? do i need a filter? ( i asshume i do) are they on 24/7, or only when water changes take place. Im completely confused!, as if i put one downstairs and connect it to my sink and ran the cables up the stairs ( in my garage, ad wont mind, i hope!) would it have enough pressure to get up them?
Thanks
Mike