Why does tap water feel different depending on the area?

Question

I live somewhere where our tap water feels kinda slimy. Every time my relatives from out-of-state visit our home, they always say that it feels like they haven’t completely washed their hands. As if there’s still soap on their hands.

I’ve noticed that in other states and countries, the tap water isn’t slimy at all. This is bad news cause I have dry skin and the water dries out my skin even more. I have no problem with my facial wash that I use on the daily when I’m at home. On vacation, it irritates my face because of the water.

In: 3

Answer 1

What you’re probably noticing re: washing your hands is water *hardness*.

Soap is, chemically speaking, a salt: it’s the result of reacting the fatty acids in fat with a base. For example, one common molecule in soap is sodium stearate, made by reacting sodium hydroxide (a base) with stearic acid (a fatty acid). The reason soap is this way is that the two halves of the soap molecules have different chemical behaviors, allowing them to both bind to fats (which don’t normally dissolve easily) and to water. That lets them help fats (and other hydrophobic molecules) dissolve in water and be washed away.

Soap itself is soluble, because sodium stearate dissolves easily in water. But depending on where you live, your tap water may contain other elements – most notably calcium – that can replace sodium and form calcium stearate, which is much less water-soluble. This calcium stearate doesn’t wash away and leaves a residue on your hands, which is probably what your relatives are feeling.

In general, we refer to water with high mineral (particularly calcium) content as *hard* water, and other water as *soft* water. Different areas have different levels of natural water hardness because they have different minerals underground, where water is found in aquifers. Areas with, say, a lot of limestone tend to have hard water. Areas with hard-to-dissolve rocks like basalt tend to have soft water.

My guess would be that you live either in Florida or somewhere in the Mountain West or western Great Plains, which tend to have hard water, and your relatives are from the east, southeast, or extreme west coast, where water tends to be softer.