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Water hardness

Hardness levels

Most of our water supply can be classified as ‘moderately hard’ (on a scale of one to ten this would be seven). 

For more information on water hardness and test results from customers’ taps in your area, please use this postcode search.

The Total Hardness Level is 270 mg per litre as Calcium Carbonate (CaCO3).  This is equivalent to:

PPM (parts per million)


Clarke Degrees

French Degrees

German Degrees





Supplies north of Ringwood receive a slightly higher hardness level of 320 mg/l as CaCO3. This is equivalent to:

PPM< (parts per million)

Clarke Degrees

French Degrees

German Degrees





What makes water ‘hard’?

Water hardness is determined by the geology of the water source. Most of our supply originates underground in chalk aquifers where it dissolves natural minerals, such as calcium carbonate – chalk hardness or limescale.

You have probably noticed this limescale inside your kettle or around your taps.

Softening treatments

Domestic treatments such as jug filters, water softeners or conditioners all have pros and cons.

Jug filters

Jug filters are jugs that have a replaceable cartridge housed in a unit that fits on top. The two main types of cartridge available have either:

  • an activated carbon media designed to remove chlorine and organics, or
  • an ion exchange resin media designed to soften the water

The carbon cartridges don't chemically alter the nature of the water but simply absorb things like chlorine. If you find black deposits in the water or the top of the jug, they will most likely have come from these cartridges, rather than our water supply.

The ion exchange softening cartridges chemically remove the calcium and magnesium salts in the water and replace them with sodium. For this reason, we advise against using this water for drinking for people on low sodium diets. We also advise against using this water for making up infant feeds. These cartridges may leave orange or white particles in the water.

It’s important to maintain and replace both types of filters in accordance with the manufacturer’s instructions. Old filters can cause a build-up of particles and encourage bacterial growth, which contaminates the water. Filtered water should be drunk soon after pouring, as water with the chlorine removed has no protection against the growth of bacteria.

Water softeners

These plumbed-in devices use salt to soften the water by removing the hardness salts (calcium and magnesium) and replacing them with sodium.

We strongly advise keeping a separate tap for un-softened water for drinking as water softened this way can contain higher levels of sodium, which is not recommended for people on low sodium diets, or for making infant feeds. It has also been suggested that people who consume softened water may suffer a higher incidence of heart disease.

Softened water is a lot more aggressive towards metal fittings. You may experience higher corrosion of pipework, and if a softening system is fitted to an older system there is a greater risk of pinhole leaking once the protective hardness layer has been removed.

Water conditioners

These devices are attached to the outside of water pipes. They do not alter the chemical composition of water, but impart some form of electric or magnetic field into the water as it passes through. In theory, this changes the crystalline structure of the hardness salts so that a hard limescale does not build up.

Despite manufacturers’ claims, it has not been possible to find a unit that works in all circumstances. If you wish to try one, choose a manufacturer that offers a full refund after a reasonable trial period in case you are not satisfied.

Press Office

Journalists can contact the Press Office on 01392 443020 or via email


Should you get a water meter?

Water meters have important benefits for you, for us and for the environment as you can have more control over your water use and leaks are easier to detect.  

Find out more

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