Advertisements by companies that provide water softening service are common. Hardness is expressed in parts per million of dissolved solids. This is almost the same as milligrams per liter. Someone accustomed to soft water with only 35 ppm dissolved solids can tell from taste, feel, and washing action that water with 125 ppm is hard. Most people would say that water at 150 ppm seems hard, and 175 ppm would trigger sales of water softeners.
Hard water shortens the service life of pipes and chemical equipment.
It is also bad for boilers, and a power plant that generates steam will always treat its water. When possible, condensate that should be essentially distilled water is fed back to the boiler. Simple softening is not enough for boiler water, and deionization by ion exchange may be used. If everyone in a community wants softened water, chemical treatment at the water works is only about one-sixth the cost of treatment at each individual household. Of course, a complicated chemical process is impractical for each home, and ion exchange is preferred.