Water is known as the 'Universal Solvent' because it is capable of dissolving more substances than any other known liquid. Wherever water goes it picks up & absorbs soluble nutrients, chemicals and minerals from whatever it comes into contact with. Water holds these trace elements in suspension & they are free to deposit onto other surfaces at a later stage.
Water is known to be hard when it contains high amounts of calcium, magnesium, manganese, iron or any other dissolved mineral which it may have picked up from layers of bedrock deep underground. These minerals are more commonly known as Limescale & can be identified by white staining on your taps & kettle or by a streaky residue left on windows, glassware & smooth surfaces in your home.
As water is used in your home, small amounts of these staining minerals are deposited onto the surfaces of anything that it may come into contact with. This is the reason why your clothes & towels may look dull after washing or why your skin may feel so dry after showering.
As water is the universal solvent it has a natural ability to dissolve household soaps & cleaners. However when water is saturated with limescale causing minerals, its ability to dissolve these soaps & cleaners effectively is drastically reduced. This poses two problems, first you must use more soap to create a decent lather & second it becomes very difficult to rinse this soap once done cleaning.