The most important details in this text are that certain types of tap water can affect skin and hair, and that testing is the best way to determine the hardness of the water. Hard water can be problematic for skin because it leaves behind dissolved minerals that may cause irritation and interact with cleanser or soap, creating a film that compromises the skin barrier and interferes with oil production. However, if you don't have dry skin or any of these issues, then tap water should not be a problem for you. Hard water can interfere with natural oils on the hair and scalp, causing it to become dry, brittle, and more prone to breakage. Copper pipes can leave behind trace amounts of the metal that affect the color of the hair over time.
Tap water may also contain chloramines or chlorine, which can dull or remove the hair color. If you live with hard water or excessive chlorine or metals, you may want to reconsider washing your skin and hair with tap water. If you're happy with the way you look and feel, don't look for unnecessary problems to solve.