Hard water has been linked to eczema in children in several studies, but the link is weak and the evidence is graded as very low certainty. Softening your water has not been shown to treat existing eczema. Nobody has shown that hard water causes skin problems in healthy adults. This guide sets out what the studies found, where they disagree, and how to check your own water. It is general information, not medical advice.
What “hard” means here
Hardness is the amount of dissolved calcium and magnesium in tap water. We report it as mg/L of calcium carbonate (CaCO₃). Higher numbers mean harder water. Hard water leaves limescale on taps and kettles. It also reacts with soap and detergent, which is the part researchers think may matter for skin.
Nothing in the water is a contaminant in this sense. Hardness is a normal result of water passing through limestone or chalk. The question is only whether it changes how skin and cleansers interact.
What the studies found
Most of the research comes from one group of UK dermatology researchers, so the picture is narrower than the number of papers suggests.
Observational studies. A 2021 systematic review and meta-analysis in Clinical & Experimental Allergy pooled 16 studies. Children living in harder-water areas had higher odds of eczema (odds ratio 1.28). The authors rated the certainty of that evidence as very low. Observational studies cannot rule out other differences between areas, such as climate, housing or diet.
Skin barrier. Two human studies in the same review found more residue of sodium lauryl sulphate, a common detergent, on skin washed in harder water. The review treats this as a possible mechanism, not a proven one.
Gene and water together. A 2020 analysis in the British Journal of Dermatology followed 1,303 infants to age 36 months. Across all infants there was no overall association between water hardness and eczema (adjusted hazard ratio 1.07, 95% CI 0.92 to 1.24). Among infants with a loss-of-function mutation in the filaggrin gene, hard water was associated with a higher rate of eczema. The authors describe this as evidence of an interaction, not a cause.
Treatment trials. The SWET trial in PLoS Medicine (2011) randomised 336 children with moderate to severe eczema. Some had a water softener installed and some did not. After 12 weeks both groups had improved, and the difference between them was not statistically significant. The authors concluded softeners gave no additional benefit to usual care. The 2021 review reached the same view for established eczema.
Prevention trials. The SOFTER pilot trial (Clinical & Experimental Allergy, 2022) installed softeners before birth in London homes with a family history of atopy. At 6 months, visible eczema was found in 33% of the softener group and 48% of controls. It was a feasibility study and was not designed to test effectiveness, so this gap is not conclusive. Larger trials would be needed.
Summary of the evidence
| Question | Finding | Certainty |
|---|---|---|
| Is hard water associated with childhood eczema? | Yes, modest association (OR 1.28) | Very low |
| Does it matter more for some infants? | Possibly, with filaggrin mutations | Single cohort |
| Does a softener help existing eczema? | No significant benefit in two trials | Moderate |
| Can a softener prevent eczema in infants? | Unknown, pilot only | Not tested |
| Effect on healthy adult skin | Not established | No good data |
What this means at home
The honest reading is mixed. Hard water may be one small factor among many for some children. It is not a proven cause, and a softener is not a proven treatment.
Some practical points follow from the research.
- Skin conditions need a clinician. If you or your child has eczema, dry or irritated skin, talk to a GP, pharmacist or dermatologist. Do not buy a softener as a substitute for medical care.
- Cleansers matter. The mechanism studied is detergent residue. Using less soap and rinsing well is a low-cost step that does not depend on your water.
- A softener has other reasons. It protects pipes, heaters and appliances from scale. That is a separate case from skin. See the water heater guide for the appliance side.
- Softened water adds sodium. Ion-exchange softeners swap calcium for sodium. If that concerns you, ask your doctor.
How hard is your water
Hardness changes from city to city, and sometimes from street to street. To find your own figure, enter your postcode in the lookup page. To see what hardness means for a specific home, the calculator converts units and estimates scale effects.
Here are a few cities with published utility figures, from our data:
| City | Median hardness (mg/L CaCO₃) | Range across zones (mg/L) |
|---|---|---|
| Berlin | 328.4 | 269.5 to 415.9 |
| Munich | 282.0 | 248.1 to 319.5 |
| Frankfurt am Main | 217.8 | 71.4 to 364.1 |
| Hannover | 214.2 | 153.5 to 232.1 |
| Hamburg | 208.8 | 91.0 to 326.7 |
| Bremen | 138.1 | 113.1 to 241.2 |
| Essen | 117.8 | not published |
| Wuppertal | 98.2 | 91.0 to 201.7 |
Other pages with zone ranges include Nuremberg (215.1 mg/L) and Duisburg (223.1 mg/L).
The SOFTER protocol defined hard water as above 250 mg/L CaCO₃. By that line, Berlin and Munich are above it, while Essen and Wuppertal are below it. Several cities, such as Frankfurt and Hamburg, straddle it depending on the zone. Our current dataset is weighted to Germany, so check the lookup page for other countries.
Frequently asked questions
Does hard water cause eczema? No study has shown that it does. Observational research finds a modest association in children, and one cohort suggests it may matter more for infants with a filaggrin gene mutation. Association is not cause, and the certainty of the evidence is rated very low.
Will a water softener clear up eczema? Two randomised trials found no significant benefit for established eczema compared with usual care. Whether softeners could help prevent eczema is still being studied. For any skin condition, see a clinician.
Is soft water better for my skin? Some people feel their skin is less dry with softened water, but there is no good evidence for healthy adults either way. Soap lathers more easily in soft water, so it is easy to use too much. Rinse thoroughly in any case.
Sources
- Jabbar-Lopez ZK, Ung CY, Alexander H, et al. The effect of water hardness on atopic eczema, skin barrier function: a systematic review, meta-analysis. Clin Exp Allergy 2021;51(3):430-451. PubMed 33259122
- Jabbar-Lopez ZK, Craven J, Logan K, et al. Longitudinal analysis of the effect of water hardness on atopic eczema: evidence for gene-environment interaction. Br J Dermatol 2020;183(2):285-293. Oxford Academic
- Thomas KS, Dean T, O’Leary C, et al. A randomised controlled trial of ion-exchange water softeners for the treatment of eczema in children. PLoS Med 2011;8(2):e1000395. PubMed Central
- Jabbar-Lopez ZK, Ezzamouri B, Briley A, et al. Randomized controlled pilot trial with ion-exchange water softeners to prevent eczema (SOFTER trial). Clin Exp Allergy 2022;52(3):405-415. Newcastle University eprints
- Jabbar-Lopez ZK, Gurung N, Greenblatt D, et al. SOFTER trial protocol. BMJ Open 2019;9(8):e027168. PubMed Central
- City hardness figures: utility sources listed on each city page linked above.