Filtered water and eczema — what the evidence actually says

What the evidence actually says

The relationship between water quality and eczema (atopic dermatitis) is a genuinely active area of dermatological research, and the evidence is more nuanced than most filter marketing suggests. There is real research supporting a link between water hardness and eczema severity. There is more limited evidence on chlorine and chloramine. Here is what is established and what remains uncertain.

Hard water and eczema — the strongest evidence

The most robust research connects water hardness to eczema. Several mechanisms have been proposed:

• Skin barrier disruption: Calcium ions in hard water interfere with the natural moisturising factors (NMFs) in the outer skin layer (stratum corneum), increasing transepidermal water loss and reducing the skin’s ability to retain moisture. This effect is well-documented in laboratory studies.
• Detergent interaction: Hard water forms calcium and magnesium soaps with surfactants in body wash and shampoo, leaving a residue on skin that can disrupt the skin barrier further. Soft water requires less detergent to rinse clean.
• SOFTWATER trial (UK, 2021): A randomised controlled trial of 336 infants found that installing a water softener did not reduce eczema incidence — but the study measured incidence (who got eczema), not severity in those who already had it. The softened water group showed trends toward less soap use and possibly reduced severity, though results were not statistically significant for the primary outcome.
• Epidemiological associations: Multiple population studies have found associations between residential water hardness and eczema prevalence in children, though these studies cannot establish causation.

Summary of hard water evidence: Biologically plausible mechanisms exist, and population associations are documented. A definitive large RCT showing symptom improvement in established eczema from water softening is still outstanding. The evidence suggests benefit is most likely in infants and young children in high-hardness areas.

Chlorine, chloramine and eczema — weaker evidence

Chlorine is a known skin irritant at high concentrations — swimming pool reactions are the clearest example. At concentrations in tap water (typically 0.1–0.6 mg/L in Australian supply), the direct irritation evidence is less established. Some eczema patients report improvement after installing a shower filter, but self-reported improvement in a condition known to fluctuate is difficult to interpret clinically.

Chloramine at tap water concentrations has not been established as a direct skin irritant in clinical research, though it remains an area of interest given its persistence in water. Several dermatologists recommend minimising chloramine exposure for patients with eczema as a precautionary measure.

By city — relative water quality concern for eczema

What filter actually helps

Based on the current evidence, the most defensible recommendations for eczema-affected households are:

For households in hard water zones (Perth, Brisbane inner, Adelaide)

A whole-home TAC or softener system addresses the best-evidenced mechanism — hard water skin barrier disruption. TAC is salt-free and maintains the mineral content of water while preventing scale. A salt-based softener produces genuinely soft water (calcium removed) and also adds sodium. Both protect appliances and plumbing. The choice between them depends on hardness level and preference.

For showering specifically: soft water typically produces a noticeably “silkier” feel on skin as it rinses clean more effectively and doesn’t leave mineral film. Many people with eczema or sensitive skin report this as a meaningful improvement.

For chloramine cities (Sydney, Brisbane, Adelaide, GWW Melbourne)

A Vitamin C shower filter neutralises chloramine (not standard KDF or carbon shower filters — these do not effectively remove chloramine). For households where chloramine exposure reduction is the goal, a Vitamin C shower filter specifically targets this. These require cartridge replacement every 4–8 weeks and cost more per year than standard shower filters.

Whole-home catalytic carbon filtration also addresses chloramine city-wide — every tap, every shower, the dishwasher. This is more comprehensive than a single shower filter but requires a plumber to install.

What not to do

• Standard KDF shower filters for chloramine cities: KDF does not address chloramine. If you’re in Sydney, Brisbane, Adelaide or GWW Melbourne and buying a standard shower filter for eczema, you are not addressing the disinfectant your city actually uses.
• Expensive alkaline or ionising filters: No clinical evidence supports alkaline water for eczema management. The pH of water has minimal effect on skin given the skin’s own pH buffering systems.
• TAC in Melbourne or Sydney for eczema: Melbourne’s water is already very soft (18 mg/L). A TAC or softener in Melbourne provides no benefit for eczema and is an unnecessary expense.

Other factors that matter more than water quality

Water quality is one factor among many in eczema management. Dermatologists consistently emphasise that these have stronger evidence and should be prioritised:

• Emollient use immediately after bathing: Applying an emollient within 3 minutes of getting out of the shower traps water in the skin before it evaporates. This has strong clinical evidence for eczema management.
• Bath or shower temperature: Very hot water (above 40°C) strips natural skin oils. Lukewarm water (35–38°C) is recommended for eczema-affected skin regardless of water quality.
• Fragrance-free products: Fragrances in body wash, shampoo, laundry detergent and fabric softener are among the most common contact allergens in eczema patients.
• Trigger identification: Environmental triggers vary significantly between individuals. House dust mites, pet dander, specific fabrics, stress, and food triggers are all worth investigating alongside water quality.