Is Hard Water Ruining My Hair?

A chemistry expert weighs in.

Have you ever visited a new city and found your hair to feel a little flat, lacklustre or just off? Perhaps after some extensive Googling you learned it may be because you’re washing your hair with “hard water.” This type of water contains a high level of minerals compared to other water, and some people claim it can cause dry, limp locks.

Is that true? Is hard water really bad for your hair? To find out, we spoke to Joe Schwarcz, a professor of chemistry at McGill University and director of McGill’s Office for Science and Society.

What is hard water?

When we talk about hard water versus soft water, we’re not describing the water’s density or feel. Water’s “hardness” refers to its concentration of minerals. “Pure water, like distilled water, is just H2O—there’s nothing else in it,” says Schwarcz. In contrast, water that’s been in contact with the ground, such as water that comes out of our taps and showers, contains dissolved calcium and magnesium compounds.

Is that bad?

It could be—at least when it evaporates: Hard water leaves behind some minerals that react with soap (specifically, glycerin and fatty acids that’s in all soap) and forms a precipitate, says Schwarcz. Precipitates are better known as soap scum—that gross white film that develops in tubs, sinks and showers.

Soap scum is actually why detergents were invented. Detergents (an umbrella term that includes shampoo and laundry detergent), are specifically made with surfactants instead of glycerin and fatty acids because those ingredients don’t react with the minerals in water and therefore don’t leave behind soap scum.

Okay, does that mean hard water is bad for my hair?

No, especially if you wash your hair with shampoo. “Shampoos were developed to counteract the reaction between minerals in the water,” says Schwarcz. And, even if you wash your hair with hard water without shampoo, “you will get a precipitate that’s going to stay behind on your hair, but it’s not going to have any effect on the growth of your hair,” he says. However, it’s possible hard water will make hair less shiny and maybe a bit weighed down because of the minerals left behind.

Are products that claim to counter the effects of hard water useful?

Some products, like clarifying shampoos and water softeners, claim to help tackle the effects of soap scum. But Schwarcz says, “it’s just a marketing technique.” As long as you use shampoo, there’s no need for special products.

Next: Why You Should Tell Your Derm About Hair Loss