HydrionisGlobal Water Intelligence
Diagram

Where hardness comes from

Hardness is geology written into water. Rain is soft everywhere; what it flows over decides what it becomes.

Where hardness comes from

Hardness is geology written into water. Rain is soft everywhere; what it flows over decides what it becomes.

Where hardness comes fromRain falls with almost no dissolved minerals. Where it flows over granite, sandstone or peat, little dissolves and the water stays soft. Where it percolates through chalk, limestone or dolomite, carbonic acid dissolves calcium and magnesium carbonate, and the water becomes hard. The result is that hardness maps closely onto underlying geology rather than onto anything about the water supplier.Rainnaturally softGranite / sandstonelittle dissolvesPeat moorlandorganic acidsChalk / limestoneCaCO₃ dissolvesDolomiteadds magnesiumSoft water<50 mg/l as CaCO₃Hard water>200 mg/l as CaCO₃
Scotland and Wales
Predominantly hard igneous and metamorphic rock, so water is generally soft.
South east England
Chalk and limestone, so water is generally very hard.
What it means for you
Hardness has no adverse health effect. It affects scaling, soap use and taste, and it is set by the rock, not by the water company.

Text description

Rain falls with almost no dissolved minerals. Where it flows over granite, sandstone or peat, little dissolves and the water stays soft. Where it percolates through chalk, limestone or dolomite, carbonic acid dissolves calcium and magnesium carbonate, and the water becomes hard. The result is that hardness maps closely onto underlying geology rather than onto anything about the water supplier.

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