Water hardness

When water falls as rain, it is "soft" and free of minerals. It picks up minerals as it passes through rock, sand and soil. 

Water supplied by Cambridge Water is all ground water - drawn from water-bearing rocks, or aquifers, under the ground. The calcuim and magnesium in the rocks causes the water to become "hard."

Hard water is high in mineral salts, especially calcium and magnesium ions. These natural minerals give the water a crisp, pleasant and fresh taste.

Calcium also forms an essential part of our diet. Most of our recommended daily amount comes from eating dairy products or bread, but drinking water also has a positive effect.drinking water 3

Some research has also shown that people who drink harder water have a better heath record with regard to heart disease.

More than 60 per cent of homes in the UK have hard water.

How can I find out about the water hardness in my area?

Sometimes it can be important to know the water hardness in your area, particularly if you are purchasing new household appliances such as washing machines or dishwashers, or fitting a new water heating system.

Cambridge Water customers can find out more about the water hardness in their area by clicking here

NOTE: The hardness of water depends on its content of calcium and magnesium salts.  When measuring the total hardness, the sum of these salts is determined and in modern day terminology is expressed in millimoles a litre (mmol/l).

Sometimes it can be important to know the exact water hardness in your area, particularly if you are purchasing new household appliances such as a washing machine or dishwasher, or fitting a new water heating system.

The following table shows water hardness in the Cambridge Water area. It shows the highest value across all of our sources. Water hardness can fluctuate across the area by a tiny amount each day; however, this fluctuation does not change the figures below.

Hardness values

Hard water in the home

In the home, hard water can lead to the furring and scaling of heating systems, kettles and household appliances such as washing machines. How much fur or scale build up usually depends on the hardness of the water, the type of system involved, the temperature to which the water is heated and how much water is used.


Using hard water in kettles produces calcium carbonate scale or fur. In metal kettles this sticks to the side and in plastic kettles, which have smoother sides, it appears as a film on top of the water.

This scale does not increase the time it takes to boil the water or the amount of fuel you need. However, we do recommend you remove it regularly.

You can do this by half filling the kettle with water and adding two tablespoons of white vinegar and leaving it for four hours, after which you can empty the kettle and remove the loosened scale. Rinse and repeat as necessary.

As an alternative you can buy a scale remover, and follow the instructions on the packet.


Many dishwashers have a built-in water softener to provide water for rinsing dishes. These remove salts which could otherwise be left as scale on drained washing up. These machines also require regular topping up with Dishwasher Salt.

toiletBaths, showers, sinks and toilets

Lime scale is the deposition of salts of calcium and other metals contained in hard water.

Thin films of limescale can form on the smooth surfaces of baths, basins, WC pans, allowing dirt to adhere. For the best results clean regularly using a liquid cleaner (abrasive materials may scratch the surface.) If the lime scale persists in your toilet you may want to regularly clean the pan with an acid-type sanitiser available from hardware stores and supermarkets,

Remember, do not mix cleaners and always ensure you read instructions carefully. 

Heating systems

There are two main types of heating systems. Direct systems are the traditional method for heating water. Water travels from a tank in the roof, to a boiler, where it is heated. The water then rises to a cylinder in the airing cupboard, where it stays until you use it. To avoid scale simply avoid overheating the water. A maximum temperature of 60oC (140F) is recommended.

Indirect systems do not tend to produce scale because of the way they are designed.  Essentially because the same water goes round the system only a tiny amount of scale is produced.

You can reduce any scaling in heating systems by using a chemical scale inhibitor, but we would suggest you take advice from a qualified plumber before using these as they can be unpleasant if they get in the drinking water system.

Immersion heaters

Immersion heaters can be susceptible to too much scale building up on the heating element and stopping the water circulating properly. We recommend you make sure the thermostat is working and correctly adjusted. For most homes 60oC is sufficient.

If you regularly use an immersion heater it may be possible to prevent the build up of scale by using elements with special metal sheaths. In some cases you may also want to use a chemical scale inhibitor, but as before we would recommend you take advice from a qualified plumber.

Magnetic and electrical scale inhibitors

There are a number of devices available in the marketplace which claim to stop scale and fur from forming. While many have been approved by the Water Regulations Advisory Scheme (WRAS) as devices that will be safe to use, this does not guarantee their effectiveness. Your own plumbing design and other local factors may influence how well the equipment works and it is wise to get a guarantee, with a money-back clause from the manufacturer in case you are not satisfied with the results.

Should I use a water softener?

Using a water softener is a matter of personal choice. While it will take care of the hard water, there are other things to consider before converting to a soft water system:

  • The initial cost of the unit
  • A water softener will increase your water usage. 
  • Expect to see a higher electric bill due to the cost of operating the unit.
  • The sodium level of the water will increase slightly, which might be a health consideration.


  • Water softeners may improve efficiency and increase the life of appliances that use hot water
  • It will make lathering easier and reduce tide marks on sanitary ware.
  • Some people with skin conditions, such as eczema, have fewer problems if they use soft water for washing

But if you do install a water softener you should make sure that you have a supply of unsoftened water for drinking and cooking.

This is because:

  • There is evidence of less heart disease in hard water areas than in soft water areas, although not all studies find this link. If something in hard water protects against heart disease, water softeners might remove this protection along with the hardness
  • Many water softeners work by replacing the hardness with sodium. Too much sodium can be a problem for premature babies because their kidneys are not good at filtering