What typically causes the temporary hardness of water?

Temporary hardness of water is primarily caused by the presence of calcium bicarbonate, which can be derived from the dissolution of calcium carbonate in water. This type of hardness can be removed by boiling the water because boiling causes calcium bicarbonate to decompose into calcium carbonate, which precipitates out of the solution. As a result, when we refer to calcium carbonate in the context of temporary hardness, it is often in its relationship with calcium bicarbonate and the reaction that occurs during the heating of water.

The other options do relate to water chemistry but do not specifically address the cause of temporary hardness. For instance, sulfates are generally associated with permanent hardness, and while chlorides do affect water quality, they do not contribute to hardness in the same way that calcium compounds do. Similarly, iron content, while potentially problematic in water supply, does not contribute to the classification of hardness as temporary or permanent. Thus, the presence of calcium carbonate is the key factor that defines temporary hardness in water.