Hard water areas
Areas rich in chalk and limestone, such as much of the South East, the Midlands, East Anglia and the North East – have hard water. The rain percolates down through the porous rock, dissolving calcium as it goes. The alkaline qualities of chalk and limestone counteract the acidity of the water, and make it less acidic.

Mountainous and rocky regions such as Scotland, Wales, the North West and the West Country tend to have softer but more acidic water. The rain quickly runs off the hard rock and is collected in lakes and reservoirs.

Three types of hardness
Temporary hardness
Caused by the presence in the water of dissolved calcium and magnesium carbonate (CACO3). It is called temporary because it can be removed from the water by heating, which causes scale to form on hot metal surfaces and is measured in parts per million (ppm).

Permanent hardness
Caused by the presence in the water of calcium sulphate, or plaster of Paris (CaSO4). This cannot be removed by heating the water, and reacts with soap and detergent to form a scum or stearate, which can be greasy, damaging and unhygienic. This is also measured in ppm, a formula is then applied and the result stated as ppm CACO3.

Total hardness
This is the sum of both temporary and permanent hardness, and is always used when calculating the size of water softeners.

How to quantify hardness
There are various ways of measuring hardness in water, including

Parts per million and milligrams per litre are the same, and ppm is now the generally accepted standard in the UK. Virtually all water analysis sheets showing dissolved elements are expressed as the CACO3 equivalent in ppm.

How to measure water hardness
The simplest and most practical way to measure water hardness is with a BWT Water Hardness Test Kit. These are sold under the brands of Aqua-Dial, Liff and Waterside, and are available from all good builders merchants and DIY stores. They are also supplied automatically with BWT manufactured water softeners.

Instructions for use
To use the kit simply fill the sample bottle supplied to the ‘fill mark’ with the water to be tested. Add one tablet from the kit to the bottle, replace the cap, and shake well until the tablet dissolves and the water turns ‘plum red’.

Keep adding tablets one at a time, counting them as you go, until the water turns dark blue. Make a note of how many tablets you have added, and refer to the instructions on the back of the test packet for results and recommended water treatment.