Minerals found in tap water include calcium, sodium and magnesium. Selenium, potassium and silica may also be found in some tap water, depending on location. The amounts of these minerals in drinking water have ramifications for health and the proper working of plumbing systems and appliances.
Calcium, potassium, selenium and magnesium are necessary for good health. There are studies that show that people who drink water with minerals in it are more hydrated than people who drink demineralized water. However, too many minerals in tap water can make the water "hard." Hard water can leave behind a material known as limescale inside plumbing pipes. Over time, limescale can become so thick that it can lower the water pressure or cut off the water flow altogether. Eventually, affected pipes will need to be replaced, which is a time-consuming and expensive job.
Limescale can also clog pipes that feed washing machines and other household appliances that use water, which can shorten the life of the appliance. Minerals in tap water can also leave laundry feeling dingy when it comes out of the wash, and can leave behind residue and rings in the bathtub and shower stall that can be hard to remove.