Chlorine is a powerful disinfectant which has been used for many years in the water industry to make water safe to drink.

Using chlorine is better than using other disinfectants as it is effective from our treatment works right up to your tap.

You may occasionally notice a chlorinous smell/taste to your water after we have made a change to our water treatment processes.

The level of chlorine dosed into your drinking water is carefully controlled and monitored.

We strive to keep the level of chlorine constant, but unavoidable operational changes at our treatment works, or within the distribution system, may result in a slight taste of chlorine.

Chlorine leaves our treatment works at less than one milligram per litre (one part per million), the level recommended by the World Health Organisation.

By comparison, water found in swimming pools typically contains 3 milligrams per litre of chlorine which produces an easily detectable odour.

Drinking water treated with chlorine poses no risk to health, but if you are concerned about the taste then a good way to reduce this is to fill a jug with water and refrigerate it overnight, to let the chlorine evaporate.

It should be noted that water kept like this should be treated as a perishable food and be consumed within 24 hours.

Domestic water filters or jug filters (both of which can contain activated carbon) can be used to remove chlorine from tap water.

These filters should be used in accordance with the manufacturer's instructions.

There is no reason to use either type of filter on health grounds, as tap water containing chlorine is perfectly safe to drink.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

Water is disinfected to make it safe to drink.

Disinfection plays an important role in protecting public health by killing harmful bacteria.

This is likely to be caused by trapped air in the pipework or dissolved chalk particles.

Air can get into the water supply following repair work on our water pipe network, or by a pocket of air becoming trapped in the pipework inside your home.

Aerated water has a cloudy or milky white appearance. This is because of the concentration of thousands of tiny air bubbles that make the water look white.

Chalk deposits arise from the natural minerals found in water and forming a fine white sediment. Drinking water supplied by us is generally described as hard, and has a higher concentration of natural minerals than soft water. The presence of suspended chalk has a powdery white appearance.

In each case, there is no risk to health although the appearance of the water may be unappealing.

To determine whether the cause is air or chalk the 'Glass Test' can be used:

• Fill a glass with water from the cold kitchen tap and watch how it clears.
• Aerated water can take up to ten minutes to clear, and will clear from the bottom of the glass upwards.
• Water containing chalk takes an hour or more to clear, with the glass clearing from the top downwards.
• A fine sediment will then be left on the floor of the glass.
• Any white water in the mains network should clear within two to three hours.
• After this time the tap should be run for two to three minutes to check that the problem has cleared.

However, if the problem persists please contact us for further advice.

It should be noted that aeration can also be caused by mixer taps or supataps forcing air into the water stream.

Water softeners

If you have a domestic water softener fitted it can release white pieces of scale over time.

It is advisable that any domestic softeners are fitted downstream of the drinking water tap, and are maintained according to the manufacturer's instructions.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

Hardness is determined by the level of naturally occurring calcium and magnesium compounds that the water contains.

Water with a high calcium and magnesium content are considered to be hard, and those waters with a low content are considered to be soft.

Hard water is found in areas which have a chalk and limestone geology.

As water passes through the rock it picks up chalk carbonates, the concentrations of which will determine the level of hardness.

There is no health risk associated with hardness.

Hardness is determined by the level of naturally occurring calcium and magnesium compounds a water contains.

Water with a high calcium and magnesium content are considered to be hard, and those waters with a low content are considered to be soft.

All supplies in the Thames Water area are generally classified as hard.

There is some variation in the degree of hardness across the area, with water in the Guildford region being the softest.

Hard water is found in areas which have a chalk and limestone geology.

As water passes through the rock it picks up chalk carbonates, the concentrations of which will determine the level of hardness.

There is no health risk associated with hardness.

However, hard water can lead to scale formation and may also affect the appearance of hot drinks, increase soap consumption and reduce detergent efficiency.

If your internal domestic system contains either copper or lead pipes then the minerals in hard water can create an internal protective film.

This protective film can line the pipes and prevent the metals leaching into the drinking water supply.

If hardness scale becomes a problem there are a number of simple measures that can be taken to reduce the level of deposition:

• Reducing the temperature of your hot water to 60°C or lower can decrease scale deposition.
• A stainless steel wire scale collector placed in your kettle can reduce scale build-up.
• In some types of plastic kettle the scale may not stick to the sides but float on the surface of the water. This can be avoided by regularly rinsing the kettle.
• Follow the manufacturers instructions for any appliances that use later.

You can find out the water hardness level for your area by entering your post code online.

• Check the water quality in your area

No - we do not add fluoride to our water.

The decision on whether to add fluoride to water supplies is taken by your local strategic health authority.

For more information on fluoride please contact your local health authority.

Fluoride occurs naturally in soils and rocks and can therefore be found in raw water.

The concentration of fluoride depends on the type of soil and rock the water passes through.

Fluoride levels in drinking water of 1 mg/l (1 part per million) are considered to have health benefits by reducing the incidence of tooth decay.

The decision to fluoridate water supplies is taken by your local strategic health authority - not by Thames Water.

Your health authority should be contacted for further details on fluoridation.

Thames Water supplies have a natural concentration of between 0.1 - 0.4 mg/l.

In the areas to the south and west of Reading the concentrations can be higher, typically around 1 mg/l.

Fluoride is not currently added to water supplies by Thames Water.

The most common cause of brown/orange/yellow water is suspended particulate iron. Small rust fragments may also be present in the water.

There are many possible sources of particulate iron found in water:

• Iron can occur naturally in some raw waters which are taken for drinking water treatment.
• Iron salts can be chemically dosed into water during treatment. It acts as a coagulant and means that the unwanted solids stick together. This makes it easier to remove them.
• Disturbance of iron deposits found along some mains. Iron deposits can be caused by the corrosion of cast iron pipes, or by dissolved iron in the water body falling out of solution. Changes within the mains network, such as vibrations through the ground or the use of a hydrant, can dislodge the particles and they move around the pipework.
• Domestic plumbing can be a source of discolouration, particularly if it has undergone recent work.

The discolouration is not harmful, but care should be taken to avoid the use of water until it has cleared.

The taste of the water may not be of the usual standard and may stain clothing.

To potentially identify the cause of the discolouration water can be compared from your cold kitchen tap (mains fed), with water from a neighbour's cold kitchen tap.

If the discolouration is isolated to your tap it may be an internal plumbing issue, but if your neighbour is also affected it may be the supplying main.

In either case, allow the system to settle for one hour and then run the affected tap for two to three minutes.

If the problem persists contact us for further advice. If the problem lies with the domestic system then we will be able to advise you on plumbing services in your area.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

Black water is usually caused by high amounts of manganese particles in the water.

Small black fragments may also be present in the water.

Manganese is found naturally in some raw waters, and is often combined with iron or chalk.

Manganese deposits may move around the water mains network if, for example, there is a disturbance to the pipework.

Black water can also be caused by hardness scale building up in domestic pipework which has been stained black by traces of manganese.

If any work is performed on the domestic water system this may dislodge these deposits into the water.

Black discolouration caused by manganese is not harmful, but care should be taken to avoid the use of water until it has cleared.

The taste of the water may not be of the usual standard and may stain clothing if brought into contact.

Under normal conditions, water will return to its usual quality after a short time.

Allow the water system to settle for approximately 1 hour, and after this time run the tap for two to three minutes to check the water is running clear.

If the problem persists please contact us for further advice.

There are two other common causes of black particles in drinking water - carbon particles from jug filters and disintegrating tap washers.

• Jug filters can contain activated carbon filters which may leak black particles into the water. Fill a glass with water from the cold kitchen tap and compare it with water from the jug filter. If the black particles only appear in water from the jug filter then refer to the manufacturer's instructions.
• If the black particles are large and can be compressed between the fingers then the fragments are likely to come from a disintegrating tap washer. The washers should be examined and replaced as necessary.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

Turquoise green/blue water is commonly caused by high concentrations of copper.

Copper is rarely present in raw waters, but may get into into water supplies from copper pipes used in internal domestic systems.

In new internal pipework/new properties a build up of hardness scale on the surface of the pipes will gradually reduce this.

In extremely high concentrations copper can give water a very unpleasant taste, and can cause vomiting.

If an internal softener is fitted it may cause the corrosion of this protective scale coating, causing an increase in the amount of copper released.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

This is often caused by high numbers of harmless micro-organisms, particularly fungi.

Micro-organisms occur naturally in all waters and their numbers increase during the summer months.

This growth can be a particular problem in domestic systems, especially if the water has been allowed to stagnate.

In addition, the warming of cold domestic pipes by the hot water system can produce conditions favourable for microbial growth.

Fungal growths or slimes may occur around taps and other water outlets, and in some cases be seen hanging from tap spouts.

Water with an earthy/musty taste has no associated health risks, although it may be unappealing.

There are a number of things you can do to solve the problem:

• If the property has been unoccupied for some time then the cold kitchen tap should be flushed for approximately five minutes and then left to stand for one hour.
• The proximity of hot domestic pipes to cold pipes should be checked, and appropriately lagged if necessary.
• Fungal growth and slimes can be removed by using a chlorine-based disinfectant. As a further measure, it should be ensured that there is an adequate turnover of water within the household system.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

This can be caused by chlorine in tap water reacting with particular substances/materials to produce new chlorine compounds.

These new compounds are often formed by the reaction of chlorine with tap washers, plastic kettles, washing machines, dishwashers, connection hoses, rubber anti-splash attachments and plastic pipework.

Advice on suitable fixtures and fittings is available from the Water Regulations Advisory Scheme who publish a list of suitable materials which do not react with chlorine.

• Visit the Water Regulations Advisory Scheme website

There is no health risk associated with this type of taste, although the water can be unappealing.

Below is a list of common issues and possible actions you can take:

• Kettles: Chlorine compounds can react with some plastic kettles. This is generally noticed when the water is boiled, and is particularly evident in new kettles. New kettles should be boiled and the water discarded at least twice before being used for hot drinks.
• Dishwashers and Washing Machines: When not in use, try closing the in-line control valves if the appliance is plumbed in upstream of the drinking water tap. Check that the machine has a non-return valve fitted. Remember to reconnect appliances before using them.
• New Domestic Plastic Pipework: This pipework can be a potential cause, and its replacement should be considered if the problem persists over an extended period of time.
• Non-Return Valves and Connection Hoses: If a non-return valve has been fitted they can wear out over time. Check on the condition of both the valve and the hose, and replace if necessary.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

This is usually caused by the domestic plumbing system where water has been left standing for long periods in metal pipework. The dissolved metals can form granules which look like sand.

If metallic domestic pipework has been installed in an order other than galvanised iron, iron, lead and copper, then metal compounds may be broken down and released from the pipework.

The fitting of a domestic water softener can cause metals from the pipework to enter the water supply, particularly if the water is very soft.

Metallic compounds are normally harmless to health unless levels have become elevated.

If you are concerned about a metallic taste and odour contact us immediately for further assistance.

Below are three suggestions which might help solve the problem: 

• Flush the cold kitchen tap if water has been left standing for long periods of time. This water can be collected in a bowl and used for purposes other than drinking and cooking.
• If a water softener is fitted, check it has been installed correctly and is operating as described within the manufacturer's instructions.
• If you have concerns over the order and type of metallic pipework in your home then it may be necessary to arrange for a plumbing inspection. We can help you arrange a pipework inspection.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

Lead is commonly found in the environment and can derive from sources such as vehicle exhaust fumes and old paint.

Lead can also be present in food, water, air and soil, and is able to accumulate over time in the human body which can have health implications.

There is essentially no lead present in the drinking water we supply as it leaves our treatment works.

The network of mains, which transports the water to your tap, are not made from lead.

However, lead pipes have been used at some individual properties to connect the domestic system to the mains.

Over time, lead can come out of these pipes and enter the drinking water supply for that property.

Additionally, lead can also be found in some solders used for copper piping.

Lead pipes were used up to the 1970's to connect individual properties to the water mains, and were also used for the internal domestic system.

If your home was built before 1970 then it may contain lead pipes, but if your home was built after 1970 then it is unlikely.

The pipe connecting the water main to your cold kitchen tap is called a service pipe and comprises of two parts - the communication pipe and the supply pipe.

We are responsible for the communication pipe and the property owner is responsible for the supply pipe. If your service pipe is made of lead we recommend it is replaced.

Who is responsible for the pipework?

In 2001, we introduced a method of dissolving the lead in the water supply at a number of our treatment works. This is known as plumbosolvency.

Since the treatment was installed there has been a significant reduction in lead concentration in many areas, and further reductions are anticipated as the treatment achieves its full effect.

UK and European regulations require water companies to test drinking water for pesticides to ensure levels are not above the drinking water standard, which is almost zero - 0.1 micro grammes per litre, which is one part per 10 billion, or one drop in an Olympic-sized swimming pool.

Most of our 25,000 annual tests show that no pesticides have made it into our treated water supplies.

However, samples do occasionally show detectable traces of weed killers like isoproturon, diuron and mecoprop, but these are almost always well below the stringent European pesticide standard.

In fact, the concentrations detected are so small that they pose absolutely no risk to public health. If they did, the Drinking Water Inspectorate wouldn't let us supply our water.

Following advances in detection methods, we've recently started to look for metaldehyde, the pesticide in slug pellets.

Traces have been detected in treated water supplies by water firms across the country at levels very slightly above the pesticide standard.

It's impossible to completely remove metaldehyde from water using normal treatment methods.

That's why we're working with manufacturers and farmers, the main users of slug pellets, to prevent metaldehyde from reaching water sources in the first place.

Experts say an average-size person would have to drink more than 1,000 litres - more than a tonne - of the worst-affected water (which is not in Thames Water's supply area) every day of their lives to exceed the Health Protection Agency (HPA)'s 'acceptable daily intake' for metaldehyde.

Pesticides include all herbicides, insecticides, fungicides, rodenticides and their related products.

Tiny amounts of pesticides can be transported by rainwater from agricultural sites, gardens, local authority sites and other sources into water catchment areas.

Pesticides can also reach drinking water sources through aerial drift and by percolation through the soil.

We have an ongoing campaign to control the use of pesticides by talking to and working with local users'.  As a result, many local organisations have modified their use of pesticides to protect water resources.

We continue to lobby for additional controls on specific pesticides that are regularly found in drinking water sources.

Water treatment steps used to remove pesticides from drinking supplies include activated carbon filtration and ozone dosing.

Activated carbon filters tightly bind pesticide compounds as water passing through them, while ozone attacks the chemical compounds and breaks them up.

These two processes can be used in isolation or as a combined approach.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

Cryptosporidium is the name given to a type of protozoan parasite which can infect humans and animals.

These parasites can be found in the faecal material of infected humans and animals and can survive in the environment for several months.

Infection with Cryptosporidium arises by ingesting the parasite. Common transmission routes include:

• Contact with infected animals (particularly cattle and sheep).
• Person-to-person spread (particularly within families/households).
• Swimming pools in this country and especially abroad.
• Other recreational waters (e.g. boating lakes, rivers).
• Contaminated food and water

Infection with this organism is called cryptosporidiosis and symptoms can persist for several weeks.

In healthy people the infection is usually self-limiting, but in immunocompromised people (e.g. people with a suppressed immune system such as AIDS patients or transplant recipients) the infection is more serious and can be life threatening.

Please consult a doctor for any medical advice relating to these issues.

Under normal operating conditions Cryptosporidium is removed by effective water treatment, principally by coagulation and filtration.

However, due to the parasites' small size and inherent resistance to chlorine, there exists a small potential that the organism could penetrate the multiple treatment barriers set in place to remove it.

To combat this, regulations were brought into force in England and Wales requiring each water company to assess their treatment works against a Cryptosporidium challenge.

Each of the Thames Water treatment works sites has undergone a comprehensive risk-assessment analysing its source water and treatment processes.

Treatment works identified as having an above average likelihood of Cryptosporidium in its source water have had additional monitoring equipment installed.

This equipment continuously monitors the water going to supply, all day, every day.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

These types of stains are usually produced by an airborne bacterium which can colonise and grow on damp surfaces (e.g. tiles, showerheads, toilet bowls and sink drains).

This bacterium, which produces a pink pigment, is a common environmental organism and thrives in warm, moist conditions.

The presence of a pink/dark grey film does not indicate a problem with the mains water quality, but is representative of a domestic issue.

Frequent cleaning of any surface that is prone to pink/dark grey staining with a chlorine-based disinfectant will remove and control the problem.

In addition, by keeping bathtubs and sinks wiped down and dry following their use will help prevent the problem.

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

The drinking water we supply is closely regulated to ensure that it is wholesome, safe, and fit for human consumption.

Chlorine, used to disinfect public water supplies, can be detrimental to fish.

A free summary report of the water quality specific to your local area is available on our website:

• Check water quality in your area

For specialist advice on breeding and caring for fish, we suggest customers should contact a local pet shop or aquarium supplier. 

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

There are several different kinds of domestic water filters and jug filters available on the market, but each type is designed to remove various compounds from tap water.

There is no reason to use these filters on health grounds, as mains tap water is of a high quality and is closely monitored. 

Water that has passed through a domestic filter should be treated as a perishable foodstuff and kept in refrigerated conditions.

This water should be consumed within 24 hours. The manufacturer's instructions for the filter equipment should be followed at all times.

Visit the British Water website for advice on the installation of filters, softeners and other devices fitted to the water supply in your home,

• Visit the British Water website

If you have any further questions, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.

Insects and aquatic invertebrates can live in raw waters that are used for drinking water supplies.

Treating the water before it is put into the mains network removes the organisms. However, there is a small risk they may enter the water supply if a water main is damaged.

These organisms can also be found in domestic toilet cisterns that are improperly sealed/installed, and can also crawl into tap spouts.

Insects/aquatic invertebrates in drinking water is unappealing, and may pose a small risk to health.

If you find any insects/aquatic invertebrates in your mains drinking water, flush the cold kitchen tap for five minutes.

If you have any further questions or concerns, please call us on 0845 9200 800 (Textphone: 0845 7200 899), 24 hours a day.