Approximately 85% of U.S. homes have hard water, meaning elevated concentrations of dissolved calcium and magnesium minerals. If you see white scale deposits on your faucets, spots on glassware, or soap that won't lather well, you likely have hard water. But what does it mean for your health, and when does treatment make sense?
What Is Water Hardness?
Water hardness is measured in milligrams per liter (mg/L) or grains per gallon (gpg) of calcium carbonate (CaCO₃). The USGS classifies hardness as:
- Soft: 0–60 mg/L
- Moderately Hard: 61–120 mg/L
- Hard: 121–180 mg/L
- Very Hard: over 180 mg/L
The EPA has no MCL for hardness. It's a secondary standard (aesthetic) at 500 mg/L for total dissolved solids. The Midwest, Southwest, and Florida tend to have the hardest water; the Pacific Northwest and New England tend to have the softest.
Health Effects of Hard Water
Despite the negative reputation, the research on hard water and human health is largely positive:
- Cardiovascular benefit: Multiple epidemiological studies suggest an inverse relationship between water hardness (specifically magnesium content) and cardiovascular disease mortality. The WHO notes this as a potential benefit.
- Dietary minerals: Hard water contributes to daily calcium and magnesium intake, though the amounts are modest compared to dietary sources.
- Skin: Some research links hard water to eczema flare-ups, particularly in children, though causation is debated.
- No known serious risks: The EPA's secondary standard exists for taste and pipe protection, not health protection.
The Pipe and Infrastructure Problem
Where hard water does cause real problems is in infrastructure:
- Scale buildup reduces water heater efficiency by up to 30%
- Clogs in pipes and appliances (dishwashers, washing machines) over time
- Increased soap and detergent usage (soap doesn't lather in hard water)
Soft Water: The Trade-offs
Softened water (processed through a sodium or potassium ion exchange) removes calcium and magnesium, replacing them with sodium ions. Considerations:
- Sodium content: Softened water can add 100–400 mg/L of sodium, significant for those on low-sodium diets or with hypertension
- Corrosion risk: Soft water is more corrosive than hard water and may leach lead and copper from pipes more aggressively. If you soften water, consider a point-of-use lead filter for drinking water.
- Better for appliances: Extends appliance life and improves soap efficiency
When to Treat Hard Water
Treatment makes sense if your water hardness exceeds 180 mg/L (very hard) and you have significant scale problems, frequent appliance maintenance, or skin issues. For drinking purposes only, a reverse osmosis filter removes hardness minerals along with other contaminants. For whole-house treatment, a salt-based water softener or a template-assisted crystallization (TAC) system (salt-free) are the main options.
Check Your Water
You can check your municipal water's typical hardness in your consumer confidence report. For wells, test directly. SafeWater also shows contaminant data for your water system: Look up your water system →