BrewWater
What is water hardness?
- water hardness
- Water hardness is the traditional measure of the capacity of water to react with soap, caused by dissolved polyvalent metallic ions — predominantly calcium and magnesium — and expressed as milligrams per litre of calcium carbonate equivalent.
Short answer
Water hardness is the traditional measure of water's capacity to react with soap, caused mainly by dissolved calcium and magnesium. It is expressed as milligrams per litre of calcium carbonate equivalent. The World Health Organization calls water below sixty soft, and above one hundred and eighty very hard.
| Measure | Value | Unit | Source |
|---|---|---|---|
| Upper bound of soft water; above this, water is at least moderately hard | 60 | mg/L as CaCO3 | World Health Organization · verified |
| Upper bound of moderately hard water; above this, water is classified as hard | 120 | mg/L as CaCO3 | World Health Organization · verified |
| Concentration above which water is classified as very hard | 180 | mg/L as CaCO3 | World Health Organization · verified |
| Taste threshold range for the calcium ion in drinking water | 100–300 | mg/L | World Health Organization · verified |
Which ions actually cause hardness?
Calcium and magnesium dominate, but they are not the only contributors. Aluminium, barium, iron, manganese, strontium and zinc all add to total hardness as polyvalent cations. In natural groundwater, calcium concentrations commonly exceed one hundred milligrams per litre while magnesium is usually lower, so calcium-based hardness generally predominates.
At what point can you taste it?
The calcium ion has a taste threshold that varies with whichever anion accompanies it. Below that range, hardness is purely a question of what happens inside your machine. Above it, hardness becomes a flavour question as well, on top of whatever it is doing to the boiler.
Where does hardness come from?
It is dissolved out of sedimentary rock, principally limestone and chalk, along with seepage and runoff from soils. This is why hardness is a property of local geology rather than of water treatment, and why two towns on the same supply network can differ substantially.