What is Water Hardness?

The simple definition of water hardness is the amount of dissolved calcium and magnesium in the water.

What is water hardness measured in?

Generally, we measure water hardness as ppm (parts per million) or mg/l of CaCO3 (Calcium Carbonate). It is calcium carbonate that is the cause of water hardness and causes the formation of limescale.

There is also an imperial measurement called grain per gallon (gpg). Here 1 grain is 64.8 mg of calcium carbonate per gallon of water (3.79 litres).

Water hardness levels:

  • 0 – 60 mg/l is regarded as soft for most purposes (some processes require far lower);
  • 61 – 120 mg/l is moderately hard;
  • 121 – 180 mg/l is hard.

Water with a mg/l greater than 180 is considered very hard.

What should be the hardness of drinking water

Experts recommend drinking water with a hardness between 60 mg/l and 120 mg/l (between 3 and 7 GPG). Drinking water with a hardness above 170 mg/l can be hazardous to health, due to the high content of calcium and magnesium in it.

It should be noted that even a small content of these elements affects the quality and taste of water, so it is worth striving for the lower limit of hardness. But it is also important not to overdo it, as excessively soft water has its own significant drawbacks.

Why is water hardness important

Water in the atmosphere picks up CO2, creating a weak carbonic acid (H2CO3). As the water falls as rain and percolates down through the rock strata, it dissolves rocks containing calcium and magnesium.

Hard water is high in dissolved minerals including calcium and magnesium, and other elements such as carbonate, chloride and sulphate which affect the type of hardness. Drinking hard water has no adverse health effects, in fact, the National Research Council (National Academy of Sciences) states that hard drinking water generally contributes a small amount towards our total calcium and magnesium dietary needs.

Many industrial and domestic water users are concerned about the hardness of their water. When hard water is heated, for example in a boiler or kettle, solid deposits of calcium carbonate can form. This scale can reduce the life of equipment, raise the costs of heating water and lower the efficiency of the boiler.

Hardness can also affect other water treatment equipment, like Reverse Osmosis units, and can clog feed pipes.

Total Hardness 

Total hardness is measured as CaCO3 and is the combined measurement of the hardness-causing elements in the water.

Temporary Hardness

Otherwise known as Bi-carbonate hardness or Alkalinity hardness. Temporary hardness is caused by calcium and magnesium in conjunction with Bi-carbonate. It can be removed by boiling the water, this drives off some of the CO2, allowing calcium and magnesium carbonate to precipitate out. The water is left softer (because some of the hardness is left behind) but still contains the permanent hardness elements.

Permanent Hardness

This is the Sulphate and Chloride Hardness. Boiling this water has no effect on precipitating the hardness out. This won’t scale the boiler or pipes, but can cause an issue called ‘foaming’ in boilers, which causes carryover of contaminants into the steam.

If you would like to find out more about what hardness is in water, get in touch with one of our consultants today.