Household water softeners operate on the ion exchange process. In this process, water passes through a media bed, usually sulfonated polystyrene beads. The beads are supersaturated with sodium. The ion exchange process takes place as hard water passes through the softening material. The hardness minerals (calcium & magnesium) attach themselves to the resin beads while sodium on the resin beads is released simultaneously into the water. No phosphates are used in this process.
Hard water treated with an ion exchange water softener has sodium added. According to the Water Quality Association (WQA), the ion exchange softening process adds sodium at the rate of about 8 mg/liter for each grain of hardness removed per gallon of water.
On the other hand, water softening additives (packaged softeners) do use complex phosphates to sequester calcium and magnesium ions.
JamesMac
(also from Toronto! go Leafs go)