You may have never thought about it, but the water you bathe with every day can hide several things.

What does “hard water” mean?

The term hard water refers to water that contains high concentrations of minerals, mainly calcium and magnesium, and is usually treated with chlorine. These minerals come from the rocks and sediments with which the water comes into contact when it circulates underground. The more dissolved calcium and magnesium the water has, the “harder” it is considered.

This hardness does not pose a health risk, but it does alter the way water interacts with the body, hygiene products, and surfaces. According to the World Health Organization (WHO), water hardness is an aesthetic, not a sanitary, characteristic, but it can affect the feel, taste, and performance of soaps and detergents (WHO, Hardness in Drinking Water, 2011).

How does hard water affect the skin?

Excess minerals interfere with the way hygiene products behave. Soaps and cleansers react with the hardness and form insoluble residues, which can remain on the skin after rinsing.

Over time, this can lead to:

• Tightness or dryness after bathing.
• Itching or mild irritation, especially in sensitive skin.
• Loss of softness or rough texture.

In addition, chlorine, which is used to disinfect water, aggravates this dryness by removing the natural oils that protect the skin. Various dermatological studies have observed that areas with harder water tend to have a higher incidence of dry skin and atopic dermatitis (Thomas et al., Journal of Investigative Dermatology, 2017).

And what about hair?

Hair also suffers the effects of hard water, though in a different way.

The minerals present in the water can deposit on the surface of the hair, altering its texture and shine. Over time, these deposits:

• Make hair stiffer and rougher.
• Increase frizz and difficulty styling.
• Reduce luminosity and softness.
• Interfere with hair treatments, which cannot penetrate the fiber.

In addition, studies have found that hair exposed to hard water has lower tensile strength, meaning it becomes more prone to breakage.

Why does all this happen?

Hard water does not clean in the same way as soft water. Minerals reduce the ability of soaps and shampoos to lather and rinse completely, leaving an invisible film of residue on the skin and hair.

On the skin, this layer can clog pores and reduce natural hydration. On hair, it acts as a “mineral barrier” that traps impurities and dries out the hair fiber. In summary, hard water:

• Is not always harmful to health, but it does affect skin and hair over time.
• Tends to dry out, dull, and make hair fiber brittle.
• Causes tightness and irritation to the skin.
• Reduces the effectiveness of soaps, shampoos, and treatments.

Understanding how water hardness works is not a technical detail; it is a way of understanding why, sometimes, your skin and hair do not respond the same way, even when using the best products.