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Water Quality

Guernsey Water aims to provide water that is safe and good to drink. Our treated water is monitored on a daily basis for bacteriological and chemical quality in line with the UK Drinking Water Regulations.  These tests are undertaken at three different stages in the water treatment process, namely at the water treatment works, at service reservoirs and at customers' taps.

Water testing at customer homes

Despite our very high standards, you may notice from time to time that your tap water looks, smells or tastes different to normal.  This is usually nothing to worry about.  Some people are more sensitive to tastes and odours than others which means they may notice a slight change whilst others may not.  Our drop-down menu below provides some explanation regarding the most commonly reported issues.  However if you have a different concern, or one that persists, please contact us on 01481 229500 or by emailing so that we can try to resolve the issue for you as quickly as possible.

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If the water clears from the bottom of the glass to the top, as it does in the below video, it simply means that there are some tiny bubbles of air in the water.  This is harmless and the water is safe to drink.
If the water clears from the top to the bottom, this could mean that there is some type of dissolved solid or sediment in the water which may need further investigation so please contact us on tel 229500 or by emailing

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If the problem is affecting your cold kitchen tap (which should be fed directly from the mains) then it's likely that the water is being affected before it reaches your internal plumbing.  The discoloration is probably caused by iron sediment that has built up over time inside older cast iron water mains.  It may be that we have been working on your water mains network, perhaps fixing a burst main, and stirred up some sediment.  If this is the reason, it's normally short-lived and shouldn't last more than 24 hours.  Although the water may not look very pleasant, these iron sediments aren't harmful.  However, to help prevent this from happening, we're continually working to refurbish or replace old pipes.  If the problem does persist please contact us on tel 229500 or by emailing  as we may need to flush the water mains to get rid of the problem for you.

If the discoloured water is coming from all cold taps except the kitchen cold tap it's likely that the water is being affected after it has entered your property and it may well be a problem with your internal plumbing. The property owner is responsible for all water pipes and facilities inside the property, and all the underground pipes within the land boundary, so a plumber may be required. If you are unsure please contact us on tel 229500 or by emailing

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Green/blue discolouration is most likely to be due to the corrosion of copper pipework in your property and is a job for your plumber.  A particular risk factor is when water is left to stagnate in newly installed pipework before a property is occupied.  The colour should disappear when the tap is run but if it persists you should contact us on tel 239500 or by emailing for advice.   
On rare occasions blue-coloured tap water can also be due to water from poorly installed toilet cisterns, which have had blue disinfectant products added to them, siphoning back into the internal plumbing.  In this case you should contact us on tel 239500 or by emailing for advice.
An algae bloom can also cause green water and properties with header tanks that are not properly maintained may be particularly susceptible to this.

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A very small amount of chlorine is added to your water during the final stage of the treatment process and ensures that the quality of your drinking water is maintained as it travels through the network to your tap.  It acts as a disinfectant and a small residual amount is usually present in the water that comes out of your tap.  Although you may sometimes be able to smell or taste the chlorine it is perfectly harmless in such small quantities and there is nothing wrong with the water.

An easy way to help reduce or remove the taste of the chlorine is to fill a clean jug with tap water and keep it in the fridge.  Not only will the chilled water taste better, it will also gradually lose the chlorine smell or taste.  Make sure the jug is kept covered to avoid other strong smells within the fridge tainting the water, and be sure to discard the water after 24 hours.

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This often tends to be more of a problem during warm, sunny weather.  This is because the naturally occurring algae living in our raw, stored water can 'bloom' whereby they are able to multiply very rapidly.  The water treatment process removes the algae but unfortunately when they die they can impart a harmless, but sometimes unpleasant, musty or earthy taste to the water which isn't removed entirely through treatment.  We do monitor the raw water quality closely to try to prevent these algal blooms before they can have an effect on the taste of drinking water and we use a range of techniques, such as blending water from different sources, to help to minimise the impact for our customers.  Filling a clean jug with tap water and keeping it in the fridge may help to make your water taste better.  Make sure the jug is kept covered to avoid other strong smells within the fridge tainting the water, and be sure to discard the water after 24 hours.

Another possible cause of earthy, musty tasting water are the black plastic pipes commonly used in the 1960s and 1970s to connect water to your home.  These pipes have alkathene in them, which can give your water a musty taste or smell.  This is not harmful and flushing the taps for a few minutes before drinking will clear any water that's been standing in your pipes and may help to improve the taste.  Of course, in the long run, you may only be able to get rid of the taste by replacing your pipework.

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A fuel leak or spill can, over time, contaminate water in plastic pipework.  If you notice that your water smells or tastes of fuel or diesel please contact us as soon as possible on tel 229500 or by emailing

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Some people describe the taste of chlorine as metallic.  For advice on the taste and smell of chlorine, please see 'your water tastes or smells of chlorine or disinfectant' above.

A metallic or bitter taste can also be associated with increased concentrations of metals such as copper or zinc commonly found in domestic plumbing systems.  The problem can often be resolved by running the cold kitchen tap for several minutes drawing in fresh water from the mains and clearing the standing water in your system.  You should notice a drop in water temperature once the fresh water is coming through.

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Plastic pipework and plastic kettles can be the cause of your water tasting or smelling of plastic.  Try running the cold kitchen tap for several minutes to draw in fresh water from the mains and to clear the standing water in your system before using the water.  Using fresh water every time you boil your kettle may also help.  If you try boiling some water in a clean saucepan and it tastes fine, this may point to your plastic kettle being the problem, particularly if it's new.  You should also ensure that all your drinking water fittings are Water Regulations Advisory Scheme (WRAS) approved.

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    Testing And Sampling

    Guernsey Water tests its treated water on a daily basis for bacteriological and chemical quality in line with the UK Drinking Water Regulations. These tests are undertaken at three different stages in the water treatment process:

    At Water Treatment Works (St Saviours, Juas and Kings Mills)
    At Service Reservoirs (Forest Road storage tanks and Water Tower, Frie Plaidy)
    At customer taps (throughout the Island)

    The tests cover a range of around 130 different parameters. In addition to this we monitor our raw water resources and Catchment Area very carefully to ensure that we can continue to supply water in line with the regulatory requirements. We publish these results on an annual basis, previous results can be found on our resources page here

    Guernsey Water also undertakes testing and sampling for customer complaints and queries as necessary.

    In 2022, the quality of the water supplied was excellent with 99.98% of tests meeting all UK and European Union standards. You can view our latest water quality report below. To view previous water quality reports please visit our resources page. 

    pdf icon Water Quality Report 2022 [478kb]

    Responsibility to our customers and the environment

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