You will be on a meter eventually Compulsory and that will cost you big time if you dont get a sub meter. Binned the Di canister two years ago ,and its not back flushed, the softener is flushed with a minimal amount of salt to protected the Ro. This it turn keeps the ro in tip top condition and pro longs its life and still makes water at low TDS this in turn prolongs the life of the resin. I only changed my resin at easter after 18 months and that was because it was reading 00.2. The amount of salt is peanuts to buy over the year.