How is permanent hardness in water best described?

Permanent hardness in water is primarily due to the presence of dissolved minerals, specifically calcium and magnesium salts, that do not precipitate out upon boiling. This characteristic sets it apart from temporary hardness, which can be removed through boiling and results from bicarbonate compounds that convert to insoluble carbonates upon heating.

The distinction that permanent hardness requires chemical means to remove is important because treatments such as adding sodium carbonate or using ion-exchange methods are often necessary to effectively reduce or eliminate this hardness. Unlike temporary hardness, which is affected by temperature changes due to the conversion of bicarbonates, permanent hardness remains unaffected by temperature, making it a more persistent problem in water supply management.

Thus, describing permanent hardness as being removed only by chemical means accurately reflects the nature of this type of water hardness, emphasizing the need for specific treatment methods rather than simply physical processes like boiling.