Water Q&A: Why can't I rinse the soap off my hands?

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Learn how "soft water" and "hard water" can affect how soap works.

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Why can't I rinse the soap off my hands?

Water Questions and Answers

The terms "soft water" and "hard water" are important here. Water is said to be hard when it has a high concentration of calcium and magnesium ions. In soft water, these are replaced with concentrations of sodium or potassium ions.

If you use hard water, you may find it is harder to get soap to lather up as you wash. On the other hand, soap lathers more easily with soft water and we can easily end up using too much. When this happens, we can end up with too much dissolved soap on our hands and it requires more water to wash it away. Hard water is actually much better at binding with the molecules in soap, allowing us to use less water to wash soap away, and making our skin feel “squeaky clean”. Soap has a harder time binding with the ions in soft water, and it can actually cling to the slightly charged surface of your skin instead of being washed away. Additionally, if you use hard water, you may find it harder to get soap to lather up as you wash. On the other hand, soft water allows soap to lather more easily, and we can end up using too much — and if we have too much dissolved soap on our hands, it requires more water to wash it away. So if you’re having trouble rinsing soap off your hands, you probably have soft water.

We’ve established that hard water does a good job of cleaning soap off our skin. However, you may still be wondering why hard water tends to leave behind a white or gray residue on bathroom surfaces after interacting with soap? This residue is soap scum, formed when the minerals in hard water react with your soap. After washing our skin we rinse the excess soap and scum off our hands and body, but how often do you rinse off your shower walls after using soap?  A trick to help prevent scum buildup is to simply rinse your shower walls after showering or bathing. (Take note, you may want to consider how much extra water you could be wasting by doing this.) Soft water doesn't create soap scum which is why some people prefer it over hard water to keep their bathtubs and appliances cleaner. In summary, hard water may make your skin feel cleaner but leave your bathtub less clean, and soft water, though it may keep your bathtub shiny, may leave soap behind on your skin.