Hard water and eczema — is your tap water making it worse?

Hard water is one of the least discussed eczema triggers, partly because it's so embedded in daily life that most people don't think of it as a variable at all. But if you live in a hard water area — and large parts of the UK do — your tap water may be actively contributing to your eczema in two distinct ways.

What hard water is

Water hardness refers to the concentration of dissolved minerals — primarily calcium and magnesium carbonates — in the water supply. In the UK, water hardness is highest in the South East, East Anglia, and the East Midlands. Parts of London have some of the hardest water in the country.

How hard water affects eczema

There are two mechanisms. The first is direct: calcium and magnesium ions in hard water react with the fatty acids in soap to form an insoluble precipitate that deposits on the skin surface rather than rinsing away cleanly. This residue disrupts the barrier's pH and acts as an irritant.

The second mechanism is indirect: the irritation from hard water disrupts the skin barrier, which increases transepidermal water loss, creating the conditions for eczema flares.

A 2017 study published in the Journal of Investigative Dermatology found that bathing in hard water significantly increased skin permeability in healthy volunteers compared to soft water.

What you can do

A water softener installed at the mains is the most complete solution. For most people, a more practical starting point is a shower filter. Bathing additives — colloidal oatmeal, emollient bath oils — create a protective film that reduces direct contact with hard water minerals.

Rinsing with filtered water on the face after washing is a low-cost experiment that can quickly indicate whether hard water is a significant factor for you.