Hard Water Science

Hard water is water containing dissolved minerals, principally calcium and magnesium. The science of hard-water personal care starts by separating water chemistry from cosmetic outcomes and from medical claims.

1. What hardness means

Water hardness primarily describes dissolved calcium and magnesium. Total dissolved solids (TDS) is a broader measurement and should not be used as a synonym for hardness.

2. What minerals can do during washing

Calcium and magnesium can interact with cleansing systems and can deposit on surfaces, including hair. In skin cleansing, mineral interactions can influence what remains on the skin after washing under some conditions.

3. Chelation

Chelating agents are ingredients that can bind certain metal ions. In cosmetic formulas, chelation is one formulation strategy for managing mineral interactions. Finished-product performance depends on the complete formula and test conditions, not the presence of one ingredient alone.

4. Hard water is not the same as hair loss or a skin disease

Evidence about mineral deposition, cleansing and hair-fibre effects should not be converted into a claim that hard water directly causes follicular hair loss or that a cosmetic product treats a medical condition.

5. How Cuore evaluates evidence

We distinguish established chemistry, external research, product testing and consumer outcomes. Numerical claims are published only when the source, units, definition, date and methodology can be traced. Cuore-specific water measurements are published only after documented sampling and analytical methods are available.

Explore the evidence

• Hard Water Lab — location and topic guides.
• Evidence & Methodology — our evidence and claim standards.
• Hard Water Personal Care — how the science translates into personal-care routines.
• Hard Water Hair Care — hair-specific application.
• Hard Water Skin Care — skin-specific application.
• What Is Hard Water?
• TDS vs Water Hardness
• What Is Chelation?