It is often thought that in regions where the water is hard, washing hair feels ‘different’. Hard water contains more dissolved salts such as calcium carbonate and magnesium sulphate. Whether these salts impact the tensile strength of hair was investigated and the study published in the International Journal of Trichology in 2013.
One batch of hair strands were immersed in distilled water and another batch of hair strands were immersed in hard water for 30 days. Thereafter, their tensile strength and elasticity was investigated using a universal tensile tester. This study concluded that there was no statistical difference in hair strength between hair immersed in hard water to those immersed in distilled water.
A later study published in the same journal in 2018 showed that hard water does reduce the tensile strength of hair. Of note is the fact that this variability in the 2 studies may be due to using ‘harder’ water in the later investigation which had a much higher mineral/salt content which affected the strength.
It is thought that magnesium and calcium, present in hard water are absorbed by the negatively charged hair and results in oxidation of hair. The more exposure results in oxidative damage (similar to oxidative damage in hair dyeing), which is directly proportional to both levels of hardness and pH of the medium (hard water). This is thought to cause weakness in the hair shaft
What can be advised it that always use a conditioner after every shampoo and never use soap for washing the scalp and hair.