Hi Ian,
I dont think you have a water softener there. I t sounds like a resin vessel, some demin resin and a filter housing. If so , you dont need the filter housing as the resin allows particulates thro and is uneffected by dirt.
The vessel will have an in and out stamped on the top. Allow tap water in the in and the resultant water should be demin ready to use on the glass.
Sean`s Tip ; dont fill the resin vessel above the shoulder, with the resin beads, it wont work correctly.
Call me on 08707 282840 if you need further help.