Our water hardness is around 3 degrees Clarke (or whatever measurement it is) and in the manual falls in set value 0, which is off. But with me changing detergent so often, all in one or normal tabs I haven't turned it off. But currently have all in one fairy and finish (around 70 of each). No matter what I will always use with rinse aid as the glasses need polishing with out it, and just CBA with that.