Fit the magnet water conditioner or reverse osmosis unit to the main water supply for the building. This is usually located beneath the kitchen sink.
Install a second water conditioner or unit to the exit pipe of the cold water tank. This is not necessary in a small house unless the water stays in a water tank for more than 24 hours.
Add additional units or magnets to the exit pipe of the hot water tank and other pipes leading to separate rooms or appliance, if necessary. This is only relevant for larger buildings.