The Water Course

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Dissolved Solids

TWC 1.02 – Hardness


The terms general hardness (GH), total hardness, and hardness are synonymous. (Recall that hard water is high in dissolved minerals.) At BH, we tend to use the abbreviation ‘GH’ because this is the established standard amongst manufacturers of water titration kits. You will need these inexpensive dropper kits in order to monitor your water’s hardness. The scientific community tends to simply use the term ‘hardness’. GH can be subdivided into two categories: temporary hardness and permanent hardness. In this video we walk you through how to calculate your water’s general hardness. 



Temporary Hardness

What Is It?

In the coffee industry, we are in the business of boiling water almost constantly. Putting water through this ordeal helps us identify the types of minerals that can be removed from water by boiling and those that cannot. Before water is heated, the dissolved minerals that have the ability to precipitate (undissolve) form what is referred to as the temporary hardness. When the water is boiled, these minerals precipitate out, reducing the hardness.

The two minerals involved here are calcium bicarbonate which is abbreviated as Ca(HCO₃)₂ and magnesium bicarbonate, abbreviated as Mg(HCO₃)₂. Both are readily soluble in water. However, when heated, the bicarbonate ion breaks down into a carbonate ion, carbon dioxide, and water. The carbonate ion binds to calcium or magnesium ions in the water and forms calcium carbonate, which is much less soluble — that means most of it will precipitate out and form a solid.


Ca2+       +     2HCO₃–      →     CaCO₃               +         CO₂          +    H₂O

(calcium + bicarbonate → calcium carbonate + carbon dioxide + water)


In practice, simply boiling water and then proceeding to brew a coffee does not guarantee that all the temporary hardness in the water disappears, as it takes a long time for all of the minerals to precipitate. As the brew water drops below 100° C,