Calcium ions are the most common ions released in the water by natural sources like calcium rocks, calcite minerals and limestone or from synthetic sources like calcium using industries. Calcium ions are found in water as bi-positively charged ions that combine with sulfate and chloride ions to form calcium sulfate and calcium chloride, respectively. These two compound are responsible for the permanent hardness in water.
Magnesium is the second largest source of water hardness after calcium. Magnesium ions are also bi-positively charged ions and are known to form compound with sulfate and chloride ions, the same way as calcium ions. Magnesium sulfate and magnesium chloride is a part of the scale and permanent hardness present in the water.
sodium ions are also responsible for bringing about hardness in the water. Sodium ions react with carbonate ions to sodium bicarbonate that can increase the temporary hardness. Sodium ions also act as a substitute for calcium and magnesium ions in hardening water.
Carbonate ions are negatively charged, tri-negative ions that combine with ions like calcium and sodium to form calcium carbonate, magnesium and sodium bicarbonate respectively. Carbonate hardness is temporary in nature and can be removed by water softening.