1. Ignore it. Usually the most expensive option when you count the cost of hard water scale damage to your hot water system, washing machine, taps, showers, irons, coffee machines, as well as higher energy costs (even 1/8inch of scale in your hot water system accounts for 20% of energy costs). Hard water marks around basins and taps, extra soap costs and the damaging effect to sensitive skin.

WARNING: 2. Buy a water softener. Costs depend on size but are between 500€ and
    2,000€ and between 30€ and 150€ a year on salt.  You also have to
    remember to fill the softener with salt and you can not drink the water.
  

WARNING: 3. Buy a magnet or other in line device. Magnets that clip on to pipes
    cost from 25€ to 100€. These are usually found to be partially effective
    and tend to work under ideal flow conditions only.  The water generally
    stays treated for only a short period and therefore to treat a whole          house a number of these are needed.
                   The effect is generally not powerful enough to remove existing scale.
                   Other in line devices are usually either ionization or catalytic and have
                   been found to suffer some of the same limitations as magnets with very
                   variable results.

4. Buy a Scalewatcher. A Scalewatcher uses the same principles as magnets but uses powerful electronic high frequency signals that are designed to effectively treat all water conditions and flow rates. The water remains treated for 5 days or more and one unit can therefore protect the whole house. Existing scale is effectively dissolved with a consequent saving in water heating costs and if you have sensitive or dry skin you will be amazed by the relief that a Scalewatcher gives you.