White discolouration in water can be caused by either trapped air or dissolved chalk particles.

• Air can be introduced into the water supply following repair work on the distribution network, or by a pocket of air becoming trapped in the internal domestic pipework. Aerated water has a cloudy or milky white appearance.
• Chalk deposits arise from the natural minerals found in water precipitating out and forming a fine white sediment. Drinking water supplied by Thames Water 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 observe 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.

Note
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.

Black discolouration is usually caused by high concentrations of suspended particulate manganese.

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 become mobilised in the 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 derive from a disintegrating tap washer. The washers should be examined and replaced as necessary.

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

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

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

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

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.

Chlorine is used in the treatment and distribution of drinking water as an anti-microbial disinfectant.

Chlorine has been used for many years as a disinfectant in the water industry to prevent the spread of infectious diseases, and has the added advantage that it remains effective from dosing right up to your tap.

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

Thames Water strives 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.

The taste will disappear by morning as chlorine is released from the water.

It should be noted that water kept in this fashion 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.

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 strategies which can be used to alleviate this taste 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.

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.

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.

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 precipitate out from the water and form granules, giving the appearance of 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.

In addition, if a domestic water softener is fitted then this could cause metals from the pipework to leach out, 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 strategies which may help to remedy 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.

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 constructed from lead.

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

Lead can leach from these pipes into the drinking supply, affecting that particular 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 to have lead pipes.

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.

Thames Water is 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 pipe work?

In 2001 a programme was initiated by Thames Water to install plumbosolvency treatment at a number of our works.

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.

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.

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.

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.

Thames Water has an on-going campaign to control pesticides at the point of use by pursuing an active and positive dialogue with local users.

As a result, many organisations have modified their use of pesticides in order to protect water resources.

Thames Water continues 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.

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.

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.

Drinking water supplied by Thames Water 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, which contains various chemical parameters for your local area, is available on our website:

Check water quality in your area

For specialist advice on fish husbandry, we suggest customers should contact a local pet shop or aquarium supplier.

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,

British Water website

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

These organisms are removed following effective treatment before the water is dispatched into supply.

However, aquatic invertebrates and insects could enter the distribution network if a main has become compromised.

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

The presence of insects/aquatic invertebrates in drinking water is unappealing, and may pose a small risk to health.

If insects / aquatic invertebrates are discovered in the mains drinking water, flush the cold kitchen tap for five minutes.

If the problem persists please contact us.