Hard Water and Your Hair: What the Evidence Actually Says

Hard water gets blamed for a lot in this part of the world. Dull hair, itchy scalp, shampoo that will not lather, the lot.

Georges Barbers has been cutting hair in Amersham since 1991, so we have heard the theory more times than we can count. It turns out some of it holds up and some of it does not, and the honest answer is more interesting than either extreme.

How do you find out whether your water is hard?

Check your own postcode with your water company, because that is the only figure that actually applies to your tap.

Every water company in England and Wales publishes hardness data for its supply zones, usually through a postcode lookup on their website. Your supplier's own figure is the one to trust. We are not going to quote a number for Amersham here, because we could not verify one from a source we were willing to stand behind, and a made up figure is worse than no figure.

What you can do without any data at all is look at your kettle. Limescale on the element, a film on the inside of the kettle lid, white marks on taps and shower screens, and soap that is reluctant to lather are all the same story. If that is your kitchen, you have hard water, whatever the number turns out to be.

Does hard water actually weaken your hair?

Nobody can tell you that with confidence, because two studies in the same journal came to opposite conclusions.

In 2013, Srinivasan and colleagues published a study in the International Journal of Trichology. They took 10 to 15 strands of hair from each of 15 volunteers, split each sample in two, and immersed one set in hard water and one in distilled water for ten minutes on alternate days across 30 days. Their conclusion was blunt: "The hardness of water does not interfere with the tensile strength and elasticity of hair."

In 2018, Luqman and colleagues published in the same journal and found the reverse. They used hair from 70 men, built three groups of 70 hairs each, treated one with deionized water and one with hard water against a control, and measured tensile strength on a universal testing machine. Their conclusion: "Hard water decreases strength of hair and thus increases breakage."

Both are real, both are published, and they disagree. Anyone telling you the science is settled on this has read one of them and not the other.

Why would two studies land in different places?

Because they were not really doing the same thing, and that is worth understanding before you decide who to believe.

The 2013 study used 15 volunteers and a soaking protocol on alternate days for a month. The 2018 study used hair from 70 men and a different treatment and measurement setup, and it sampled water from ten districts to find its hard water sample. Different sample sizes, different water, different methods, different results.

That is not a scandal, it is what a young evidence base looks like. The practical takeaway is that if hair damage from hard water exists, it is not so large and obvious that it shows up unmistakeably in every study. Which is itself useful to know, because it means hard water is probably not the main thing wrong with your hair.

What does hard water definitely do?

It leaves more of your shampoo behind on your skin, and that is the part with the strongest evidence behind it.

Danby and colleagues, publishing in the Journal of Investigative Dermatology in 2018, found that "sites washed with hard water had significantly increased sodium lauryl sulfate deposits". Sodium lauryl sulfate is one of the most common detergents in shampoos and washes. Those deposits then "increased transepidermal water loss and caused irritation", and the effect was strongest in people with atopic dermatitis carrying particular genetic variants.

Read that again, because it reframes the whole argument. The problem is not the water attacking your hair. The problem is the water stopping the detergent from rinsing away cleanly, and then the detergent sitting on your skin irritating it.

That maps neatly onto what people actually complain about. Not snapping hair, but a tight, itchy scalp and hair that feels coated and lifeless.

So is it the water or the shampoo?

Realistically it is the combination, and the shampoo is the half you can change tomorrow.

If hard water is leaving more detergent on your skin, then the amount of detergent you start with matters. Using less product, rinsing for longer than feels necessary, and not doubling up on a second lather out of habit will all reduce what is left behind. So will using a gentler formulation, if your scalp is the thing complaining.

This is also why so many people find their hair feels different on holiday and assume it is the sun. Different water, different residue.

What is actually worth changing?

Start with the free changes, then spend money only if they do not work.

• Rinse longer than you think you need to. This is the single change that follows directly from the Danby findings, and it costs nothing.
• Use less shampoo. Most men use more than they need, and in hard water more product means more residue.
• Skip the second lather unless your hair is genuinely dirty rather than just habitually washed twice.
• Turn the temperature down a little. Hot water is hard on skin regardless of hardness.
• Deal with the scalp separately if it is itching or flaking, because that may be a different problem entirely. We covered that in the autumn scalp guide.

Does hard water cause hair loss?

This is the question underneath a lot of the others, and the honest answer is that none of the research above went anywhere near it.

The two trichology studies measured tensile strength, which is how much force a strand takes before it breaks. The dermatology study measured detergent deposits, water loss through the skin and irritation. Not one of them measured shedding, thinning or hair loss. So when you see hard water confidently blamed for hair loss, that claim is not coming from these papers.

Breakage and hair loss are also different things that feel the same in the shower. Hair snapping partway along the shaft leaves short broken pieces and is a condition problem. Hair coming away from the scalp with the root attached is shedding, and the causes for that are almost entirely elsewhere. If you are seeing genuine thinning, that is a GP conversation rather than a plumbing one.

Do water softeners and shower filters help?

The evidence for softening is real but narrower than the marketing suggests.

The Danby study found that "water softening by ion-exchange mitigated the negative effects of hard water" in their experiment. That is a genuine finding and it is the strongest thing anyone can currently say in favour of softening. It is worth being clear about the limits though: that result is about detergent deposits on skin and the irritation that follows, measured in a controlled study, not a promise about how your hair will look.

If you already have a softener for the kettle and the boiler, you will probably notice your shampoo lathering more easily and rinsing more cleanly, and that is consistent with the research. If you are considering installing one purely to improve your hair, the honest position is that the evidence does not stretch that far.

Shower filters are a different product making similar claims, and we have not seen research of that quality supporting them. We are not going to tell you they work.

What can a barber actually do about it?

Cut in a way that hides the symptoms while you sort out the cause.

Hair that feels coated and heavy tends to sit flat and look duller, and that shows up worst on longer, one length styles. A shape with a bit of texture through it, or a little more weight taken out, moves better and catches light better even when the hair itself has not changed at all.

If your hair has genuinely become brittle and is snapping mid-length, that is worth saying out loud in the chair. There are a lot of causes for that and water is only one of the candidates, but a barber looking at it closely can usually tell you whether the damage is at the ends, where a cut fixes it, or all the way up, where a cut does not.

Booking, walking in and where to find us

Walk in any day of the week for a haircut, skin fade or beard trim at 11 Chesham Road. No appointment needed.

If you want a set time, book online Monday to Friday. Ear piercing is the one service that always needs an appointment booked in advance.

Full details are on the haircuts page and the skin fades page, and men travel in from Amersham, Little Chalfont, Chalfont, Chesham, Beaconsfield, Gerrards Cross and High Wycombe.

Sources

• Srinivasan G, Srinivas CR, Mathew AC, Duraiswami D. Effects of hard water on hair. International Journal of Trichology, 2013.
• Luqman MW, Ramzan MH, Javaid U, Ali R, Shoaib M, Luqman MA. To Evaluate and Compare Changes in Baseline Strength of Hairs after Treating them with Deionized Water and Hard Water and its Role in Hair Breakage. International Journal of Trichology, 2018.
• Danby SG, Brown K, Wigley A, Chittock J, Pyae P, Flohr C, Cork M. The Effect of Water Hardness on Surfactant Deposition after Washing and Subsequent Skin Irritation in Atopic Dermatitis Patients and Healthy Control Subjects. Journal of Investigative Dermatology, 2018.

By the team at Georges Barbers, cutting hair in Amersham since 1991.