From hair treatments to shower filters, a wave of products have been launched promising to protect hair from the “problems” caused by living in a hard-water area. But are they really necessary? “Hard water has a higher concentration of dissolved minerals, especially calcium and magnesium,” says Desmond Tobin, professor of dermatological science at University College Dublin. “These are naturally occurring in water, particularly water that is not rainwater.”

When water moves through soil and rocks, such as limestone, minerals dissolve into it and remain there when it comes out of your tap. These minerals are responsible for the limescale that builds up in your kettle.

“You know you’re living in a hard‑water area by how easy it is to lather up soap,” says Tobin. “If it is really difficult, and it forms a kind of scum rather than bubbles, you’re in a hard-water area. It’s healthy to drink, but it can trigger some issues.”

Washing your hair in hard water can leave mineral deposits on the hair shaft, which some believe make it look duller and feel rougher. There is evidence that calcium and magnesium can accumulate on hair washed in hard water, although the evidence that this causes damage is less clear.

Removing this buildup can cause problems, though, especially for those with dry or brittle hair. Tobin says the best shampoos for doing so are high lather and contain ingredients such as sulfates, which can be harsh on those hair types. “It’s this balancing act between removing the buildup and leaving enough oil in the system to condition the hair,” says Tobin.

If you live in a hard-water area and notice your hair getting drier, Tobin recommends installing a water softener in your home.