What are the effects of hard water on hair?

Tap water is naturally rich in minerals, including calcium and magnesium. When their concentration is high, we talk about hard water or limescale-rich water. This limescale comes from the dissolution of limestone rocks through which the water passes during its natural cycle. Water hardness varies greatly by region and is measured in French degrees (°f). The richer the water is in calcium (Ca²⁺) and magnesium (Mg²⁺) ions, the harder it is considered. While this mineral content is not problematic for health, it can interact with the surfactants in cleansing products and leave deposits on the skin or on the hair fiber. It is in this context that the question of the link between hard water and hair arises, especially when one observes changes in texture or shine after washing.

Although it is often said that hard water damages hair, the mechanisms involved deserve clarification. During washing, the calcium and magnesium ions in hard water can interact with the surfactants in shampoos and gradually deposit onto the surface of the hair fiber. These mineral residues then alter the hair’s electrical charge, affect its surface, and can disrupt the cohesion of the cuticle scales. Over time, this buildup can increase roughness and reduce shine, hence the widespread notion that hard water makes the hair dry.

To better understand the concrete impact of hard water on hair fibers, an experimental study compared hair strands washed for 30 days with either hard water or distilled water. Fifteen volunteers provided hair samples that were divided into two groups: one exposed to water containing 212.5 ppm of CaCO₃, and the other to low-mineral water (10 ppm).

Scanning electron microscopy analyses revealed that hair washed in hard water exhibited a more irregular, “rough” surface with significantly higher mineral deposits.

The average calcium content reached 0.804% in hair exposed to hard water versus 0.26% with distilled water, while the magnesium concentration was 0.34% compared to 0.078%. Notably, the average thickness of fibers treated with hard water was lower than that of hair washed with distilled water, suggesting a possible structural alteration.

These results therefore support the idea that hard water and hair are incompatible, particularly due to the gradual accumulation of mineral deposits on the fiber surface.

Building on these observations, another study focused not on surface appearance but on the mechanical strength of hair exposed to hard water. 73 volunteers living in a region with soft water provided hair samples, each split in two: one half was exposed to particularly hard water for three months, the other to deionized water. The researchers then measured tensile strength. The results show a significant reduction in the tensile strength of hair treated with hard water. In other words, repeated exposure to highly mineralized water appears to weaken the hair fiber and promote breakage—without directly causing hair loss.

Finally, a third study confirmed these findings by simultaneously comparing untreated hair, hair exposed to deionized water, and hair subjected to hard water. Seventy participants provided hair samples divided into three groups (control, deionized water–treated, and hard water–exposed), and tensile strength was measured. The results showed that the average tensile strength of hair exposed to hard water was significantly lower than that of both the control and deionized water groups, whereas no difference was observed between the control and deionized water groups.

These findings therefore reinforce the notion that repeated exposure to mineral-rich water can weaken the hair fiber and increase the risk of breakage, even though this does not necessarily translate into hair loss strictly caused by hard water.

Beyond the hair fiber, hard water can also interact with the scalp. Studies on the epidermis suggest that repeated exposure to calcium-rich water can disrupt physiological calcium signaling, which is essential for proper keratinocyte renewal. In the skin, calcium follows a precise gradient between the deep and superficial layers. Disrupting this balance could alter cellular cohesion and weaken the skin barrier. When applied to the scalp, this mechanism could promote irregular flaking, increased sensitivity, and, in some individuals, hard-water-induced scalp itching. Moreover, by reducing soap solubility, hard water promotes the formation of insoluble residues that may remain on the scalp surface, locally alter the pH and disrupt its comfort.

Regarding the dandruff in hair caused by hard water, some researchers suggest a possible indirect link: by weakening the skin barrier and leaving mineral residues, hard water might create a setting conducive to more visible flaking. However, it is important to note that dandruff is primarily linked to the proliferation of yeasts of theMalassezia genus and to individual factors, rather than to hard water alone. Similarly, some individuals report greasy hair due to hard water, implying that it would boost sebum production. Nevertheless, to date, no scientific evidence indicates that hard water affects the sebaceous glands. The sensation of heavier hair may instead be explained by the accumulation of mineral deposits that alter its texture to the touch, without actually greasing the scalp.

There are simple solutions to protect your hair from limescale and limit the buildup of mineral deposits. The objective is twofold: to reduce contact with calcium and magnesium ions and to mitigate their effects on the hair fiber and scalp. Here are the main strategies you can adopt:

• Install an anti-scale filter on your shower : These devices reduce mineral concentration during rinsing and offer a long-term solution to hard water.

• Use an anti-limescale shampoo or a hard water shampoo occasionally : These formulations often contain chelating agents capable of capturing calcium and magnesium ions to remove mineral deposits from the hair.

• Perform a mild acidic rinse (for example with a diluted apple cider vinegar solution) : This traditional method provides an effective approach to addressing hair mineral buildup by sealing the cuticles and reducing surface roughness.

• Regularly apply an anti-limescale hair treatment (for example, a nourishing mask) : This type of product reinforces the lipid barrier of the hair fiber and compensates for the loss of softness when hard water makes hair dry.

• Adapting the routine for textured hair : The effects of hard water on curly or coily hair can be more pronounced, as these hair types are naturally drier. Regularly moisturizing and protecting hair fibers with masks and serums can thus be particularly beneficial.

In practice, we recommend combining preventive measures (filtration, appropriate rinsing) with restorative care (moisturizing and protective treatments) to limit the effects of limescale on your hair.

• RANGACHARI S. C. & al. Effects of hard water on hair. International Journal of Trichology (2013).

• RANGACHARI S. C. & al. Scanning electron microscopy of hair treated in hard water. International Journal of Dermatology (2015).

• JAVAID U. & al. Effect of topical application of hard water in weakening of hair in men. Journal of the Pakistan Medical Association (2016).

• AYYAS M. & al. To evaluate and compare changes in baseline strength of hairs after treating them with deionized water and hard water and its role in hair breakage. International Journal of Trichology (2018).

• CORK M. & al. The effect of water hardness on surfactant deposition after washing and subsequent skin irritation in atopic dermatitis patients and healthy control subjects. Journal of Investigative Dermatology (2018).