What is Water Hardness?

Hard water  is due to the presence of calcium and magnesium and is formed when water passes through or over limestone or chalk areas and calcium and magnesium ions dissolve into the water.

Hardness is given in terms of the equivalent quantity of calcium carbonate(CaCO3) in milligrams per litre(mg/L) or parts per million(PPM).

Effects of Hard Water

You can often tell if you have hard water simply by looking at your kettle as it causes limescale build up on the element. In addition, hard water interferes with the lathering properties of soaps and detergents, and may also leave a film on tiles, windows, and walls.

You may ask, “Is Hard water bad for me?”. In terms of your health, no it doesn’t pose a problem and can even be beneficial.

However, hard water in the home can:

  • build up in pipes causing water flow and pressure to drop, and eventually pipes will need to be replaced.
  • build up on geyser and kettle elements, damaging them and causing you to have to replace them sooner, as well as reducing heating efficiency of water which will increase your electricity consumption.
  • reduce lathering properties of soaps and detergents, so you use more of these products causing you to spend more.

Hard water in Industry:

  • It will cause build up of limescale in pipes causing reduced flow and cause pipes to need to be replaced.
  • Hard water in cooling towers can reduce the effectiveness of heat transfer, causing increased running costs. It can also cause corrosion in the towers, leading to costly repairs or replacement of cooling towers.
  • In boilers and similar machines, it will build up and reduce the heat transfer, pushing up operational costs. It also causes the need for more costly maintenance and repairs, and will reduce the lifespan of the boiler.
  • In the textile industry, it can make yarn stiff/scratchy. It can also affect the colour of the clothes.


Even if you have hard water, it isn’t the end of the world. There are different methods of softening water, depending on how much water is required.

The main method for small to medium output is to use a water softener. The process starts by the hard water going through a resin bed. The calcium and magnesium cations here are exchanged for anions such as sodium. Soft water then passes through to point of use. The resin has an exchange capacity, and once this is reached, the resin must be regenerated. Salt is used for this process, and once the resin has been regenerated, the system is ready to go again.

For larger outputs, Reverse Osmosis is used. The process works whereby the hard water is forced though a semi-permeable membrane under pressure, leaving the hardness behind. A special clean may be required every now and then to remove any organics or carbonates that may be fouling the membrane.

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