Hard water has a high concentration of minerals, and of these calcium salts are the most troublesome. But there is a solution coming in form of a cheap diy water softener system built with the well-known 555 IC. Actually the price of this diy system is so low that even if this doesn’t work you won’t be upset.
The working principle of the water softener is based on a theory from 1930 which states that an electromagnetic or electric field causes small crystals of calcium carbonate in the water to join together to form larger crystals.
One of the methods to obtain a strong magnetic field is to put a powerful magnet (2.5 gauss) near the water pipe. The second method is the electronic one. Studying a water filter purchased from stores we found that it produces a frequency of about 15 kHz at an amplitude of 15V.
UPDATE: If the water pipe is metallic then connect the open ends of the coils to the pipe, or if it is made of plastic connect each open end with a conductive wire (copper).
Extension: water softener power indicator
The values of the coils are not known, but my guess is L1 has 9 turns and L2 has 7 turns. Actually you should consider this circuit as a theoretical one.
Therefore this water softener system uses one 555 IC to obtain a rectangular signal that is applied to the water pipe by wrapping two coils with one open ending around it. The coils must have good isolation. Make sure to power the water softener from a isolated power supply because in some areas the water pipes are connected to ground.