What can any material that forms a precipitate with soap be generally called?

The material that forms a precipitate with soap is generally referred to as hardness, specifically water hardness. Water hardness is primarily caused by the presence of divalent metal ions, such as calcium and magnesium, in the water supply. These ions react with soap to form an insoluble precipitate, which is often observed as soap scum. This phenomenon indicates that the water contains hardness minerals, and their presence can affect both the efficacy of soaps and detergents, as well as contribute to scale buildup in plumbing systems and appliances. Recognizing hardness is essential in water treatment and management, as it influences water quality and household cleaning effectiveness.