Hard water is a common problem affecting residential water supplies. Even the best water treatment plants can’t prevent it, since most hard water minerals enter the water after it has left the treatment plant and is on its way toward homes. The minerals of hard water (primarily magnesium and various calcites) seep through the ground and into the freshwater pipes.
Hard water isn’t unhealthy to drink. In fact, you want some amount of these minerals in your water because they’re essential minerals for good health. But too high a level of these minerals is bad for the plumbing in a house and creates inconveniences with cleaning and bathing. It can even wreck important water-using appliances; the water heater is especially susceptible to damage due to hard water.