Hard water contains dissolved calcium and magnesium. It is usually a maintenance and efficiency issue, not evidence that the mains water is unsafe.
What hardness means
Rainwater picks up minerals as it moves through rock and soil. Supplies drawn from chalk and limestone areas often contain more dissolved calcium and magnesium than supplies from other geology. When hard water is heated or evaporates, some minerals form visible deposits.
The Drinking Water Inspectorate classifies hardness expressed as milligrams per litre of calcium carbonate: soft up to 100 mg/L, slightly hard from 100 to 150, moderately hard from 150 to 200, hard from 200 to 300 and very hard above 300.
Signs around the home
- White deposits on taps, shower screens and tiles.
- Scale inside kettles and on heated elements.
- More detergent needed to produce lather.
- Marks on sinks, baths and sanitaryware.
These signs are useful clues, but they do not replace a supplier report or a correctly performed test.
Hardness is not contamination
Hardness has no prescribed drinking-water standard in UK regulations. A sudden change in colour, taste or smell is a different issue and should be raised with the water supplier.
Your next step
Find the hardness value for your supply zone, convert it to a consistent unit and decide which inconvenience you actually want to solve. A filter for taste and odour is not the same as an ion-exchange softener.
Sources and further checks
- Drinking Water Inspectorate: Water hardness and hard water
- GOV.UK: Check the quality of your drinking water
Sources are provided for verification. Product specifications and local supply information can change, so check the current primary source before acting.