Hard water is water with high levels of dissolved minerals, and usually occurs in areas where limestone and chalk are common.
These minerals can be divided into two types, and so hardness is often considered in two categories – permanent and temporary water hardness.
So how can we measure water hardness? Can we measure temporary and permanent hardness separately?
Types of Water Hardness
Water hardness can be considered in 2 types; permanent and temporary hardness.
Temporary hardness is so called because it can be reduced by simply boiling the water. This causes the bicarbonate minerals (calcium bicarbonate or magnesium bicarbonate) to form solid deposits, such as those seen on kettle elements, and so the amount left in the water is reduced.
Permanent hardness can only be removed by ion exchange processes, like those employed by water softening systems. This type of hardness is caused by sulphate minerals (calcium sulphate and magnesium sulphate / sulfate).
Measuring Water Hardness
There are a range of kits available to measure hardness, from simple test strips, to drop count kits right through to electronic colorimeters, but all of these will simply measure the hardness present, they cannot tell the difference between permanent and temporary hardness.
To do this the sample should be tested before and after boiling.
The hardness after the sample has been boiled is the permanent hardness, and temporary is easily calculated by;
[hardness before boiling] – [hardness after boiling] = [temporary hardness]