Hard water, simply, is water that contains a high amount of minerals, namely calcium and magnesium. Those minerals can change your skin’s pH balance, which can then affect your skin microbiome (remember: Our skin microbiome prefers a slightly acidic pH of about 5). “Hard water tends to make skin drier and more sensitive, and it can leave your skin reddened,” says board-certified dermatologist Loretta Ciraldo, M.D., FAAD, especially if your skin barrier is already compromised (say, if you have sensitive or eczema-prone skin).
However, assessing your skin shouldn’t be the only way to tell if you have hard water; dry, itchy skin can stem from a range of concerns, and it doesn’t always shed light on the shower. That said Ciraldo mentions a simple, at-home test to figure out if your water is hard: