These cartridges power the Manor Duo system. The NuvoH2O Manor Duo system retains the healthy 'hard' minerals in your water. Rather than removing and replacing hard water minerals (mostly Calcium and Magnesium) with sodium or potassium like old-fashion softeners do, NuvoH2O's proprietary citrus-based softening formula, CitraCharge®, bonds to these minerals making them incapable of sticking to pipes and surfaces.