Hardness · in your tap water

Hardness (calcium + magnesium)

Skin / hair / eczema · soap scum · appliance wear

Reviewed by Tyler Griffin — Founder, SwiftPro Heating, Cooling & Plumbing

FamilyHardness

Where it comes fromLimestone and dolomite geology (most of NOVA)

Best fixSalt-based ion-exchange water softener (whole-home, the only reliable solution)

What it is

Hardness measures the calcium and magnesium dissolved in your water, expressed in grains per gallon (gpg). Most of NOVA tests above 7 gpg — high enough to noticeably strip skin oils, leave soap residue, and shorten the life of every water-using appliance in your house.

If your kid's eczema flares after every shower and you've tried every lotion, the water is the variable nobody tested.

What you might notice & the health concern

Itchy or dry skin after showers — studies associate hard-water areas with higher rates of infant eczema, though they have not proven hardness causes it
Brittle or dull hair, dandruff that won't quit
Soap that won't lather, residue on shower glass and dishes
White scale buildup on faucets, kettles, and inside the water heater
Coffee that tastes off, reduced water-heater lifespan

What actually removes it

Salt-based ion-exchange water softener (whole-home, the only reliable solution)
Salt-free 'conditioners' reduce some scaling but don't actually remove hardness
Reverse Osmosis (RO) removes hardness from drinking water but not whole-home

Not sure which system you need? Our reverse-osmosis and whole-home pages compare the options, or book a free Home Water Checkup and we'll test your actual tap.

The research

Every source below was checked to make sure the link works and backs the claim it's next to. These are the primary regulators and peer-reviewed studies — not our opinion.

Hardness of Water ↗ U.S. Geological Survey (Water Science School)

Defines hardness, the soft/hard classification, and that it's 'not a health concern.'

Secondary Drinking Water Standards: Guidance for Nuisance Chemicals ↗ U.S. EPA

Hardness is an aesthetic 'secondary' concern with no enforceable health-based limit.

Hardness in Drinking-water (background document) ↗ World Health Organization

WHO sets no health-based guideline value for hardness.

Home Water Softening — Frequently Asked Questions ↗ Minnesota Department of Health

Grains-per-gallon conversion, the >7 gpg softener threshold, and the ion-exchange mechanism.

Association between domestic water hardness and atopic dermatitis in early life ↗ Perkin et al., J. Allergy Clin. Immunol. (2016)

Associates hard water with higher infant-eczema rates — associational, not proof of cause.

Want to know if it's in YOUR water?

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This page is general water-quality education, not medical advice. Health classifications and limits are attributed to the EPA, EWG, IARC, ATSDR/CDC, WHO and the cited studies. Contaminant levels vary by water system and home — the only way to know what's in your water is to test it. Prepared by SwiftPro Heating, Cooling & Plumbing.