Water is the one part of a shower nobody thought to question. You research the shampoo, read the ingredient list on the back of the shower gel, and then you rinse all of it off with whatever comes out of the tap. Except that the water is doing something too – even if just what hasn’t been given a name. There’s a good chance you experienced the effects of hard water before you ever heard the term. You know it as the chalky ring that reappears on your shower screen days after you scrubbed it off,...