Guide
Is hard water bad for you?
Safe to drink, harder on skin and pipes, and softening adds sodium.
Short answer
No, not to drink. Hardness is dissolved calcium and magnesium, and the World Health Organization has found no convincing evidence that it harms health; both are nutrients. Its real costs are scale, dry skin and dull hair. If you soften it, each grain per gallon removed adds about 7.9 mg of sodium per litre, which matters for anyone on a low-sodium diet.
What hardness is
Hard water carries dissolved calcium and magnesium picked up from limestone and chalk. It is not contamination: the same minerals are in milk, nuts and green vegetables, and hard water can supply a small share of them. The hardness scale sets out the levels.
Skin and hair
Where hard water does make a difference is the skin. Calcium reacts with soap to leave a film that can dry skin and dull hair, and some studies have found an association between hard water and eczema in young children. The hard water, hair and skin page covers what is known and what helps.
Softened water and sodium
A salt-based softener swaps the calcium and magnesium for sodium. The amount follows directly from the chemistry, so it can be worked out exactly:
| Hardness removed | Sodium added | Per day at 2 L |
|---|---|---|
| 5 gpg | 39 mg/L | 79 mg |
| 10 gpg | 79 mg/L | 157 mg |
| 15 gpg | 118 mg/L | 236 mg |
| 20 gpg | 157 mg/L | 315 mg |
| 30 gpg | 236 mg/L | 472 mg |
At 15 gpg that is about 236 mg a day from drinking water, against the 2,300 mg daily limit in the US dietary guidelines: small for most people, worth knowing on a sodium-restricted diet. The usual fix is to leave the kitchen cold tap unsoftened, or use a potassium chloride softener salt.
Where hard water does cost you
Scale shortens the life of water heaters, kettles and dishwashers and cuts water heater efficiency, and hard water needs more soap and detergent. Whether that justifies a softener is an economic question, not a health one: do I need a water softener works through it.