What effect does hard water have on hair?

Hard water contains high levels of minerals, primarily calcium and magnesium, which can adversely affect the condition of the hair. When hair is washed with hard water, these minerals can build up on the hair shaft over time, leading to a variety of issues. This mineral build-up tends to make the hair feel dry and brittle, as it can weigh the hair down and prevent moisture from being properly absorbed. Additionally, the presence of these minerals can hinder the effectiveness of shampoos and conditioners, making it difficult to achieve clean, manageable hair.

In contrast, the other options suggest beneficial effects that are not associated with hard water. For example, hard water does not enhance shine or softness, nor does it improve the natural elasticity of hair or enhance color; rather, it contributes to dullness and can even cause color-treated hair to fade more quickly due to the interaction with the minerals present.