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Water quality

Key information

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

The files listed below give key information about water quality:

Background

We supply drinking water to 430,000 people in parts of Dorset, Hampshire and Wiltshire. This number increases significantly during the summer months with the influx of visitors to the area.

Most of the supply comes from the Rivers Avon and Stour, and the remainder   comes from boreholes at Stanbridge, Wimborne, Hale and Lymington.

Safe, good quality water

A dependable source of safe drinking water is essential to life. Early methods of purifying drinking water without disinfection were only partially effective against the resilient microbes that can cause cholera, typhoid fever and dysentery.

When chlorination was used as part of properly designed water treatment systems in the early 1900s, these diseases were effectively eliminated. As a result, we have seen the UK annual death rate from waterborne diseases drop from 40 per 100,000 at the beginning of the 20th century to none. The standards of treatment and management mean that the water supply in the UK is among the safest in the world.

In order to provide you with safe, good quality drinking water we look after water quality from the source, through treatment and finally, at your tap.

Analysis and monitoring

Water quality is highly regulated. Our dedicated team carries out thousands of tests, taking samples 365 days a year from treatment works, reservoirs and customer taps to ensure that our water meets the required standards.

The result of any test is only as good as the sample taken, so a sample taken from a customer’s tap with defective plumbing, for example, could count as a ‘failure’ against the standards.

Sampling is almost a science in its own right, with over 30 types of sample containers and a wide range of techniques.

Microbiological testing provides an important measure of water quality and any non-compliance is taken seriously. We analyse water samples for bacteria of the coliform group, which occur naturally in large numbers in soil and vegetation. These bacteria outlive many harmful bacteria and are therefore a sensitive indicator of water quality. If they are found in drinking water, it indicates that there is the potential for other harmful bacteria to be present.

However, as bacteria are so widespread, their presence may indicate a problem with the sampling, rather than with the supply. If a sample does indicate the presence of coliforms, we immediately test more samples and investigate the circumstances.

Water hardness and treatment

Hardness levels

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

You have probably noticed this calcium carbonate inside your kettle in the form of scale. Very small crystals can also form a scum on top of hot drinks.

Most of our water supply is classified as "moderately hard" (on a scale of one to ten this would be seven). 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
270 19 27 15

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
320 22 32 18

If you are not happy with the hardness of the water, you might consider some form of treatment, such as jug filters, softeners or conditioners. However, all these systems 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 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, 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 both types of filters in accordance with the manufacturer’s instructions. Dirty 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 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 send some form of electric or magnetic pulse 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.

Drinking Water Inspectorate reports

The Drinking Water Inspectorate (DWI) was established by the Government to monitor the performance of water companies in providing safe and wholesome drinking water, and to ensure that all water companies meet the requirements of the stringent legislation.

Each year, the Chief Inspector of Drinking Water publishes a report on drinking water quality. 

These reports are produced on a regional basis.The latest DWI water quality report is available here.

 

 

 

 

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