Hard water refers to water with a high mineral concentration. It can cause soap and detergent not to lather properly. It can also stress the plumbing in your house. Hard water leaves a white or gray film on your body and leaves a calcified ring in the bathtub. Solutions for hard water problems range from housewide solutions to more localized treatments for each specific situation.
One of the simplest procedures for mitigating hard water issues in the bath is to add some baking soda to the bathwater. Depending on the hardness of the water, you will need anywhere from one teaspoon to 1/4 cup of baking soda to soften the water effectively. You can mix it directly into the bathwater or you can mix it with water first to form a paste and help it dissolve more quickly.
Specialized bath salts
Some bath salts also soften water. The box should say if whether a particular product softens hard water. Some companies make bath salts that are specific hard water additives. This has the added effect scenting your bathwater. There is some evidence that epsom salts also act as a water softener. Epsom salts also has health benefits, helping with bruising and muscle soreness.
Vinegar can also work as a water softener in your bath. Adding a cup of vinegar to the bathwater will soften it and also help soften your skin. The downside to vinegar, of course, is that you will likely also smell like vinegar when you leave your bath. You can counter that by rinsing in plain water, but that defeats the purpose of avoiding coating your body in hard water. You could compensate by using a heavily scented shower gel.
Bath oil may soften water as well. Simple baby oil would work, so there is no need to acquire expensive or specialized bath oils. Add just a small amount of oil to the bathwater to prevent your hair and body becoming overly oily. The advantage of bath oil is that it will also work to soften and moisturize your skin. You can accentuate this effect by rubbing bath oil into especially dry areas of your skin before getting into the bath.