Hard water refers to water that has a high level of minerals in it, particularly magnesium and calcium. Different areas of the world have different levels of hard or soft water, each of which can have impacts on the skin and hair. In general, soft water is preferred to hard water, as the effects of hard water on hair and skin can be negative. Hard water can really dry out the hair and make it more difficult to fully rinse out the shampoo and conditioner after every shower. This can cause buildup in the hair, making it look dull, and making the scalp dry and itchy.
The immediate effect of hard water on hair is that it will simply make it more difficult to manage. Many people with hard water find that their hair becomes tangled very easily, and is difficult to comb or brush out. These tangles and knots make it more difficult to wash the hair as well, and small amounts of soap and shampoo will likely remain in the hair. This causes grease and film to build up on the hair and on the scalp, causing the hair appear very dull and lifeless. As this buildup continues to increase, it just exacerbates the overall problem.
Another effect of hard water on hair to consider is that this type of water is very harsh on the hair. People who color their hair, perm it, or otherwise treat it may find that these treatments wash out very quickly. This can then lead to more frequent hair treatments, further drying and damaging the hair. Some people find that the effects of hard water makes their hair to become thinner in appearance or more prone to breakage. If not, hard water combined with frequent hair treatments typically leads to dandruff and an itchy scalp.
There are a few ways to mitigate the impacts of hard water on hair. Some people add water softeners to their home water systems in order to reduce the minerals in the tap water throughout the whole home. Some find that using clarifying shampoo once or twice a week helps to remove buildup, though for people with an especially dry scalp, this might not be a good idea. It generally takes some trial and error using different types of shampoos and conditioners to find the combination that works best with hard water; there are some shampoo products available that are specifically designed for use in hard water.