Hard water contains high levels of mineral ions such as calcium and magnesium. It doesn't only leave limescale on appliances; it also interacts with the skin surface.
When hard water combines with soap or certain cleansers, more residue can form on the skin. Observations also suggest that washing with hard water increases post-wash tightness for some people — varying by individual and skin sensitivity.
Practical approaches: use gentle, pH-balanced cleansers (which leave less residue with hard water), prefer lukewarm water, keep washing brief, and moisturise with barrier support afterwards. Some people choose shower filters; this is a personal preference.