WATER
Hard water and pool water: what they do to your hair
In short
Hard water left more cleanser on skin and about three times the calcium on hair, a surface effect. Green tints are usually copper. Pool water can strip the cuticle and bleach pigment: 61% of elite swimmers had discoloured hair.
What you need
Do this
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1
Wear a swim cap or tie hair up.Why
Rinse and wash soon after swimming.
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2
Hard-water area? Rinse longer, and consider a water softener for itchy skin.
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3
Use a clarifying shampoo every few weeks, then condition.
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4
Green tint on blond hair is usually copper; ask a hairdresser about EDTA shampoo.
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5
What the science points to: chelating rinses likely lift calcium.
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6
What the science points to: it is possible that wetting hair before swimming helps.
The numbers behind it
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3x
More calcium on hair soaked in hard water for 30 days than in distilled water (0.80% against 0.26%).
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80 people
Skin washed with a sulfate cleanser in hard water kept more of it and was more irritated. Softening helped.
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21-42%
Less calcium in chemically treated hair after citric acid, in lab tests on hair samples.
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61% vs 0%
Of 67 elite swimmers had discoloured hair, against 0 of 54 controls. Chlorine was found inside the hair.
For your hair
Blond, bleached or dyed hair
Pale hair shows copper first. Damage, frequent chlorinated water and alkaline shampoos make green tints more likely.
Regular swimmers
Cap, rinse, mild shampoo, conditioner. The worst hair in the study had lost its cuticle completely.
Itchy, flaky or eczema-prone scalp
The strongest irritation from hard water was in people with atopic dermatitis and filaggrin changes. Rinse well; consider softened water.
Curly and dry hair
If lengths feel coated, a clarifying wash then a rich conditioner is a sensible reset.
Myths to ignore
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Myth Hard water makes your hair fall out.
Truth Not supported. Studies soaked cut hair in hard water and found more calcium and magnesium and a ruffled surface: a change to the strand, not the follicle.
Srinivasan 2016 ↗ -
Myth Chlorine turns blond hair green.
Truth Copper does. Case reports found copper from pool or household water, helped along by damaged hair, chlorinated water and alkaline shampoos.
Mascaro 1995 ↗ -
Myth Swimmer's hair is just dryness.
Truth In elite swimmers, golden hair had lost its cuticle, had fewer pigment granules and held chlorine inside them.
Nanko 2000 ↗
Go deeper
- Hard water and hairHard water leaves calcium on hair and can irritate skin; the studies measure fibres and skin rather than hair loss, and chelants such as EDDS cut metal damage in lab models.
- Swimming, chlorine and green hairHeavy swimming can strip and discolour hair, and green tints usually come from copper rather than chlorine itself.
- Water temperature and hair washingSkin data favour lukewarm water, because hot water raised skin water loss and redness more than cold did; cold-rinse shine is a popular belief.
All studies in this guide (5)
Srinivasan G et al. Scanning electron microscopy of hair treated in hard water. Int J Dermatol. 2016
Tested: hard water (about 212 ppm CaCO3) versus distilled water, 10 minutes on alternate days
Result: Hard-water hair carried more calcium (0.804% versus 0.26%) and magnesium (0.34% versus 0.078%), had a ruffled cuticle and slightly smaller thickness (72.78 versus 78.14 micrometres).
Read the study ↗Danby SG et al. The Effect of Water Hardness on Surfactant Deposition after Washing and Subsequent Skin Irritation in Atopic Dermatitis Patients and Healthy Control Subjects. 2018
Tested: SLS washing in water of different hardness
Result: Hard-water sites retained more SLS, with higher water loss through the skin and more irritation, most strongly in people with filaggrin gene mutations.
Read the study ↗Zhang D et al. Reinforcing chemically treated human hair with citric acid. 2025
Tested: citric acid treatment
Result: Citric acid reduced calcium in chemically treated hair by 21-42% and improved mechanical properties.
Read the study ↗Nanko H et al. Hair-discoloration of Japanese elite swimmers. J Dermatol. 2000
Result: 61% of swimmers had hair discoloration versus 0% of controls; affected hair had lost its cuticle, had fewer melanosomes, less sulfur and detectable chlorine.
Read the study ↗Mascaro JM Jr et al. Green hair. Cutis. 1995
Result: Green tints in blond hair came from copper in household or pool water, favoured by prior hair damage, chlorinated water and alkaline shampoos.
Read the study ↗