Boiling water can precipitate some temporary hardness associated with bicarbonates, but it does not remove all hardness minerals or practically soften water for a household. In fact, limescale inside a kettle is evidence that some minerals are being deposited as the water is heated.
Hardness is not one single substance
Calcium and magnesium occur in different chemical forms. Some carbonate hardness can precipitate during boiling while other dissolved salts remain, so boiling is not equivalent to a water softener.
The mineral deposit stays behind rather than disappearing
During boiling, some carbonate forms the white scale on the kettle or pot. Pouring off water without sediment can reduce some temporary hardness in that small batch, but the mineral deposit still has to be cleaned.
It is not practical treatment for showers, laundry, or plumbing
Boiling household water would consume large amounts of energy and would not address permanent hardness. For whole-home scale problems, measure hardness first and then consider treatment designed for that flow rate.
For drinking, hardness is usually a quality and maintenance issue
Hardness can affect taste and create deposits, but it should not automatically be treated as contamination. If there is a separate health concern, targeted water testing is more useful than routine boiling.
Sources
- U.S. Environmental Protection Agency (EPA) — WaterSense Home Maintenance — Household water maintenance, leaks, fixtures, and efficiency.