Is Hard Water Bad for You?
The World Health Organization has not set a limit for it. Its 2011 background document on hardness in drinking water concludes that there are insufficient data to suggest either minimum or maximum concentrations of minerals, and so no guideline values are proposed.
WHO says hardness is caused not by a single substance but by a variety of dissolved metal ions, predominantly calcium and magnesium, and that water below 60 mg/l of calcium carbonate is generally considered soft, 60 to 120 mg/l moderately hard, 120 to 180 mg/l hard and above 180 mg/l very hard. It says hard water can cause increased soap consumption and scale deposition in pipes and heated water appliances, reducing the efficiency of heat exchangers, that excessively hard water can also have corrosion tendencies, and that the taste threshold for calcium is in the range of 100 to 300 mg/l, though higher concentrations are acceptable to consumers.
On heart health, WHO says most studies of drinking water hardness have been ecological studies reporting an inverse relationship between water hardness and cardiovascular mortality, but that weaknesses in that study design limit the conclusions that can be drawn. It says the evidence for a protective effect of magnesium or hardness is being debated and does not prove causality.
Sources checked September 15, 2026. Every point below links the page it came from.
The sources behind this answer
- Government sourceWHO says water hardness is caused by a variety of dissolved polyvalent metallic ions, predominantly calcium and magnesium, although other ions such as aluminium, barium, iron, manganese, strontium and zinc also contribute. World Health Organization, Hardness in Drinking-water (2011) ↗
- Government sourceWHO says water with calcium carbonate below 60 mg/l is generally considered soft, 60 to 120 mg/l moderately hard, 120 to 180 mg/l hard, and more than 180 mg/l very hard. World Health Organization, Hardness in Drinking-water (2011) ↗
- Government sourceWHO says hard water can cause increased soap consumption and scale deposition in water systems and heated water applications, and that excessively hard water can also have corrosion tendencies. World Health Organization, Hardness in Drinking-water (2011) ↗
- Government sourceWHO says the taste threshold for the calcium ion is in the range of 100 to 300 mg/l, depending on the associated anion, but higher concentrations are acceptable to consumers. World Health Organization, Hardness in Drinking-water (2011) ↗
- StudyWHO says most studies of drinking water hardness have been ecological studies reporting an inverse relationship with cardiovascular mortality, and that weaknesses in that study design limit the conclusions. World Health Organization, Hardness in Drinking-water (2011) ↗
- Government sourceWHO concludes that evidence for a protective effect of magnesium or hardness on cardiovascular mortality is being debated and does not prove causality, and that no guideline values are proposed because data are insufficient. World Health Organization, Hardness in Drinking-water (2011) ↗
Sources checked September 15, 2026. A brand statement is the company’s own claim, which we report but have not verified. Our grades are model-based estimates, not lab tests.