What are the differences between total hardness, general hardness and KH, and why does hardness matter?
In water, you have various ions that cause “hardness”. Usually, this is the carbonate ion such as is found in calcium carbonate, magnesium carbonate etc. When you have an ion exchange resin or pillow, all it will do is swap them for sodium carbonate, so that the hardness is no longer detectable by the same tests, but there are still carbonates found in water in a different form, so it’s not any softer in reality. This is why people often say don’t bother buying softener pillows but if you REALLY want to soften water use another way like filtering over peat, or just live with the water you get out of the tap. Originally, hardness was a measure of the ability of water to precipitate soap, and this is affected by calcium and magnesium compounds. Therefore, total hardness – and also “general” hardness – is a measure of all the calcium and magnesium salts in the water, such as (but not limited to) calcium carbonate and magnesium carbonate. Carbonate hardness (KH) is a measure of all the car
