Old thread revival maybe but then this section is quiet.... FWIW I run a Daqua 15 litre vessel with MB115 resin. I just run it inline with the pressure washer pre and rinse completely uneconomical but whatever. Spend maybe £70 a year on resin, one bag lasts for 2 fills of my vessel and typically lasts me 6 months washing once every 2 weeks. Apparently you can re-activate it.
Bought it because I owned a Megane RS with Black wheels (and then an E92 M3 with Black wheels) which used to look awful when water in the recesses for the nuts and inside the wheel rim dried and left mineral deposits.
Thinking about getting a storage tank so I can filter water into it rather than leaving the vessel standing there as I think its wasted like that.
Really helps with water spotting in the summer too, can rinse a clean car in the middle of summer in bright sunshine and just leave it to air dry with no streaks. Some next level Voodoo.