In Mexico, talking about water almost always leads to discussions about availability crises or contamination, but we rarely consider its composition. However, beyond how much water we have, what kind of water we use matters. Hard water —which contains high levels of minerals and some chemicals— is present in a large part of the country and has effects on your daily life that go far beyond the pipes.

Water hardness largely depends on the amount of minerals dissolved as it flows through the subsoil. In Mexico, approximately 70% of the supply comes from aquifers, meaning that the water passes through layers of limestone and clay rock rich in minerals. It is precisely this contact that raises the concentration of calcium and magnesium, turning the water into "hard" water.

According to data from the National Water Commission (CONAGUA) and regional studies, a large part of the central and northern regions of the country show high levels of hardness:

• In states such as Guanajuato, Querétaro, and Aguascalientes, values often exceed 250 mg/L of calcium carbonate (CaCO₃).
• In Jalisco, Chihuahua, Coahuila, and Nuevo León, even higher concentrations have been reported, in some cases exceeding 400 mg/L.
• Even in Mexico City, water from deep wells can be classified as very hard, with values around 200 mg/L.

According to international scales, any water above 180 mg/L is considered very hard. This means that a large part of the Mexican population showers, washes clothes, and cleans their home with high-hardness water without even knowing it.

Water hardness does not pose a direct health risk —it does not cause diseases or is considered a contaminant— but it does modify the way we interact with it. In the home, it is responsible for limescale formation, stains on faucets, and reduced detergent effectiveness. On the body, it influences how hygiene products behave: soap doesn't lather the same way, shampoo doesn't rinse completely, and skin or hair can feel drier or rougher. Various dermatological studies have observed that regions with harder water tend to report a higher incidence of dry skin, irritation, and atopic dermatitis, especially in arid climates. The explanation is simple: water minerals deposit on the skin surface and alter its natural balance. In hair, this same phenomenon causes stiffness, loss of shine, and increased fragility over time.

In cities where hardness exceeds 300 mg/L, the effects are even more visible outside the body: faucets with limescale, showers with white residue, and clothes that feel rougher after washing. These are domestic signs of a geological phenomenon occurring beneath our feet, but which ultimately affects our daily lives.

Understanding water hardness in Mexico is to take a closer look at an invisible phenomenon that accompanies us every day. It is a reminder that water quality is not only measured by its purity, but also by its composition; and understanding that composition is the first step to better adapt to it and take care of what we value most: our skin, our hair, and our health.