....yes i think thats true, cementone is only 10% so you're paying for 90% water. Probably not high strength enough to re-charge the anions. You can buy Hydrochloric on ebay thats 36% proof....that will do it.
Agree it does seem a faff especially if you're only paying £1.50/week, my resin costs are a bit more than that, besides I think if you can crack a recharge why not scale it up so you're recharging other peoples aswelll....then it's a business that generates it's own revenue stream....