Hardness of water is caused by the presence of calcium and magnesium ions in the water. These ions can come from a variety of sources, including runoff from agricultural fields, industrial and domestic waste, and from underground rock formations.
To rectify these causes, a variety of methods can be applied. For example, water softening systems can be installed in households to remove the calcium and magnesium ions from the water. This is done by passing the water through a bed of resin beads which have a negative charge, and the positively charged calcium and magnesium ions are attracted to the beads and removed from the water. Additionally, reverse osmosis systems can be used to filter out dissolved minerals in the water. Finally, treatment plants can be used to reduce the levels of calcium and magnesium in the water. These plants use chemicals such as sodium carbonate to convert the hardness-causing ions into a form which is not harmful.