The Water Course

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Dissolved Solids

TWC 1.07 – Recap and Glossary



  • The process of water dissolving mineral salts, e.g. calcium carbonate, makes the ions dissociate.
  • After a mineral salt is dissolved, the ions that they were made of are no longer bonded with each other and exist freely in the water
  • The process of water dissolving CO2 from the atmosphere introduces many new H+ ions into the water which makes it more acidic
  • A pH of 7 is neutral. An acidic solution has a pH below 7 and an alkaline solution has a pH above 7.
  • When water dissolves minerals, some of them can be removed from the water by boiling it. The minerals that can be removed are referred to as the temporary hardness.
  • The temporary hardness is made up of the more complex ions called calcium bicarbonate and magnesium bicarbonate. The bicarbonate ions are made of the mineral ions of calcium or magnesium, dissolved CO2, and water
  • When water is boiled the reaction releases CO2 as a gas and also makes calcium carbonate precipitate. This means limescale forms on your coffee equipment
  • The alkalinity of your water is its buffering capacity
  • The buffering capacity of water is mainly due to carbonate and bicarbonate ions
  • Heating water doesn’t remove all your water’s bicarbonate and carbonate ions straight away so they still have a chance to interact with coffee flavour
  • Too much buffer in your water makes your coffee’s acidity taste very muted and boring
  • At BH we think the upper limit for buffer in water for coffee is 70 milligrams per litre
  • The general hardness (GH) of your water is the combined amount of calcium and magnesium ions. This measurement doesn’t consider what these ions might be bonded with, it is just the total.
  • If you subtract the carbonate hardness (KH) from your total hardness, you get a measurement called the permanent hardness.
  • Permanent hardness is the amount of calcium and magnesium ions in the water that aren’t removed by boiling the water.