The 3M Aqua-Pure AP430SS system installs BEFORE the hot water heater in order to filter the water before it reaches the hot water heater.
3M Aqua-Pure Whole House Scale Inhibition Water Treatment System AP430SS
AquaPure 3M Purification Replacement Water Filters - CUNO
AQUACREST Replacement for Aqua-Pure AP430SS Hot Water filter
Aqua Pure Scale Inhibition System User Manual
Aqua Pure Scale Inhibition System
3 Pack Cartridge Fits 3M Aqua-Pure AP431,KleenWater KW431 AP430SS by AQUA CREST
AQUACREST AP431 Replacement Cartridge for Aqua-Pure AP431, AP430SS, Whole House Water Scale Inhibition System
Aqua-Pure Scale Inhibition System: 2 Years Later
3 Pack Cartridge Fits 3M Aqua-Pure AP431,KleenWater KW431 AP430SS by AQUA CREST