Why Is Soft Water Slippery?

Why does tap water treated with a water softener feel slippery?

—Joe Zagara, Rancho Santa Fe, California

Hard water often has an unpleasant taste, hampers the ability of soaps to dissolve and can cause scaling in pipes. Yet so many of us have grown up with it that we conflate the pleasure of cleanliness with the result of bathing in hard water: feeling “squeaky clean.” But the “squeak” is caused by a film of soap curd—the same residue that accumulates on our shower walls. When we switch to soft water and the squeaky feeling disappears, we think the soap isn’t rinsing off. But the opposite is the case. The lack of “squeak” means the soap curd is gone, and the soft feeling is hydrated skin.

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