Rainwater or chemically treated water is considered to be ______?

Rainwater or chemically treated water is classified as soft water because it contains low concentrations of ions, particularly calcium and magnesium, which are responsible for water hardness. Soft water is typically free from the minerals found in hard water, making it an ideal choice for various cosmetology applications such as hair washing and skin care, where maintaining moisture balance is important. Soft water can help in producing lather more easily and does not leave mineral deposits that can accumulate on hair or skin.

In contrast, hard water has high mineral content, specifically calcium and magnesium, which can create scale buildup in appliances and make it more difficult to lather soaps and shampoos. Hygienic water, while important in a cosmetology setting, does not specifically denote the water's mineral content. Mineral-rich refers to water that has high levels of minerals, which does not apply to rainwater or most chemically treated waters that are intended to be soft. Thus, the classification as soft water is the most accurate.