What causes temporary hardness in water?

Temporary hardness in water is primarily caused by the presence of calcium bicarbonate. This type of hardness can be removed through boiling, which precipitates the calcium carbonate out of solution, allowing it to be filtered out. The solubility of calcium bicarbonate is affected by temperature; when water is heated, it converts to calcium carbonate, which is insoluble in water. This is the key characteristic that differentiates temporary hardness from permanent hardness, which is caused by substances like calcium sulfate or magnesium sulfate, and cannot be removed by boiling.

In this context, while magnesium chloride, iron sulfate, and sodium bicarbonate may interact with water quality, they do not contribute to temporary hardness. Magnesium chloride and iron sulfate can affect water properties but are related to different hardness classifications or other water quality issues. Sodium bicarbonate can add mild buffering capacity but does not create temporary hardness in the same way that calcium bicarbonate does. Thus, calcium bicarbonate is the correct answer for defining the cause of temporary hardness in water.