Water Softeners
These work by forcing the water through a resin bed. The harmful calcium and magnesium ions stick to the resins and are replaced with harmless sodium ions. When the resin bed becomes clogged with calcium the system is regenerated by flushing it through with a salt solution. This clears away the calcium deposits, and recharges the resin with sodium ions. All water softeners work in this way, but have different kinds of controls to regulate the regeneration process.

Time clock:
These are the cheapest to buy, but the most expensive to run. The clock is set to regenerate the system every few days irrespective of how much water or salt has been used.

Automatic on demand:
This type of control measures how much water has been used in the home and decides when to regenerate automatically - usually at night when the household is asleep.

Automatic on demand
with proportional salt usage:
This is the same as the previous system, excpt that it works out how much salt to use based on the amount of water used each day. This saves both salt and water.