How we test your water

A chemical intermediate and solvent. It can contaminate groundwater
beneath industrial sites. Where necessary, special treatment to remove
solvents is used. Limit: 3µg/l

Alkalinity, like hardness, comes from the rocks through which water has
passed. It is an indication of the natural hardness and pH of the water. It can be altered by softening. Limit: None specified

Aluminium occurs naturally in some source waters and is removed during water treatment processes such as coagulation and filtration. As aluminium sulphate it can be used as a treatment chemical to remove particles or cloudiness. Its use is closely controlled. Limit: 200µg/l

Ammonia occurs naturally in the environment as ammonium salts and may be present in trace amounts in water. Ammonia is a key component of fertilisers, and its presence can indicate possible contamination. Ammonium salts do not themselves cause health problems and are generally removed through standard treatment, but they can interfere with disinfection processes if not treated effectively. Limit: 0.5mg/l

These substances are rarely present in water although trace levels have
been associated with impurities from plumbing. The standards for these
are generally very stringent to reflect their potential toxicity. Strict controls, monitoring and processes are in place and these substances are considered low risk. Limit: 5µg/l

These substances are rarely present in water although trace levels have been associated with impurities from plumbing. The standards for these are generally very stringent to reflect their potential toxicity. Strict controls, monitoring and processes are in place and these substances are considered low risk. Limit: 10µg/l

Not present in uncontaminated drinking water. Benzene is an organic
solvent used in a variety of industries and as an additive in petrol. It has been identified as a carcinogen. Limit: 1µg/l

A PAH compound (see total polycyclic aromatic hydrocarbons) that has a
standard as an individual substance based on its toxicity. Strict controls,
monitoring and processes are in place and the risk of its presence in the water supply is considered low. Limit: 0.01µg/l

Boron can be present naturally at low concentrations and is not considered a health risk in drinking water. Higher concentrations may be present in some surface waters where there are discharges present from industrial sources as boron is used in a variety of industries such as medical, cosmetic and agricultural preparations. Limit: 1mg/l

A by-product of disinfection formed by the reaction of naturally occurring bromide with strong oxidants, particularly ozone. A stringent standard has been set based on toxicity and best water treatment practice. Ozone is not used in our region. Limit: 10µg/l

These substances are rarely present in water although trace levels have been associated with impurities from plumbing. The standards for these are generally very stringent to reflect their potential toxicity. Strict controls, monitoring and processes are in place and these substances are considered low risk. Limit: 5µg/l

Calcium and magnesium are naturally occurring minerals found, for example, in limestone and chalk rock. Both are essential elements for health and contribute to the natural hardness of water, particularly calcium. Limit: None specified.

Chloride in drinking water originates from natural mineral salts. The most common are hardness salts – calcium and magnesium. It may be present in water from local use of de-icing salt. Chloride is not harmful to health at levels found in drinking water. Limit: 250 mg/l

It is a legal requirement to disinfect water during treatment to remove or kill harmful bacteria. In our region chemical disinfection with chlorine is a critical part of this process. Dosing is continuously monitored at every treatment works. The amount dosed is intended to ensure protection as treated water travels to your home. Chlorine reacts readily with other substances in water so that total chlorine is the total amount of chlorine present in the water while free chlorine is the proportion that remains unreacted. Limit: No limit. World Health Organisation (WHO) guidance for free chlorine between 0.2 and 0.5 mg/l

These substances are rarely present in water although trace levels have been associated with impurities from plumbing. The standards for these are generally very stringent to reflect their potential toxicity. Strict controls, monitoring and processes are in place and these substances are considered low risk. Limit: 50 µg/l

Clostridium perfringens is a spore forming bacterium present in the gut of warmblooded animals. It is commonly found in soils and the environment.
The spores remain viable for long periods and can survive disinfection. The presence of spores in drinking water indicates a remote or intermittent source of contamination that requires investigation. Tests for clostridia in treated water are taken at water treatment centres, following work installing new or repairing water mains and when investigating potential microbiological incidents. Limit: 0 per 100ml

Coliforms are bacteria that are widely distributed in the environment, often as a result of human and animal activity but also in association with soil and vegetation. Their presence in treated water supplies indicates a quality problem and a need to investigate for a source of contamination which if detected at a customer property this could involve looking into their home plumbing system. They do not themselves generally cause harm to health but indicate whether water treatment, especially disinfection, is satisfactory. Limit: 0 per 100ml

Colony counts tests provide information on the background levels of bacteria usually of environmental origin. These bacteria are generally harmless and occur naturally in soil, air, and water. Results from these tests are collated to provide an overall picture of microbial water quality and assist in maintaining the efficiency of treatment and integrity of distribution networks. Limit: No regulatory limit. Any significant change is investigated.

Colour occurs naturally in surface water sources and is removed during water treatment processes. Treated water is required to be clear, bright, and free from colour. This standard is set primarily for aesthetic reasons. Limit: 20º Hazen

This measurement is obtained by passing an electric current through the
water. It is a measure of the amount of mineral salts the water contains. Limit: 2,500 µS/cm at 20C

Copper occurs naturally in foods and the environment. In drinking water
copper arises mostly as a result of copper pipes and fittings in household
plumbing. This is especially true of new pipework where copper can result in blue or green staining of taps and other fittings and impart a sharp taste to water Limit: 2mg/l

Cryptosporidium and giardia are protozoan parasites that can infect humans causing gastroenteritis. The parasites are shed into the environment as oocysts. Where there is a significant risk from their presence in water supplies, barrier treatment processes or UV treatment are required to remove them, and strict hygiene procedures are followed to prevent their entry after treatment. Limit: No specific standard, risk assessment required.

These substances are rarely present in water although trace levels have been associated with impurities from plumbing. The standards for these are generally very stringent to reflect their potential toxicity. Strict controls, monitoring and processes are in place and these substances are considered low risk. Limit: 50µg/l

These bacteria are found in the gut of all warm-blooded animals. They should not be present in drinking water and immediate action is required to identify and remove the source of faecal contamination. Tests for enterococci are applied at customers’ taps, when proving new or repaired mains and when investigating potential microbiological incidents. Limit: 0 per 100ml

E. coli is a bacterium present in the gut of all warm-blooded animals. They should not be present in drinking water and immediate action is required to identify and remove the source of faecal contamination. They are sometimes found in untreated water, especially surface water reservoirs that provide wildlife habitats. Whilst on their own these bacteria generally cause no harm to health, their presence in water supplies indicates the potential presence of pathogens. Limit: 0 per 100ml

Traces of fluoride occur naturally in many water sources, particularly
groundwater. Fluoride is not added to any of our drinking water supplies but one source in Wiltshire has natural levels of around 1 mg/l. Fluoride is not removed by conventional water treatment. Responsibility for a decision to add fluoride as a protection against tooth decay rests with national government. Customers are advised to contact their primary care trust for further information. Limit: 1.5 mg/l

These are organic compounds sometimes present in surface water sources due to the activity of certain microorganisms and algae. When present they cause musty or earthy odours and tastes at very low concentrations. They can be removed by appropriate activated carbon treatment and are not harmful to health. Limit: No regulatory standard

Hydrocarbons are the main components of fuel, oil and solvents, and
cover alkyl benzenes, benzene, toluene, and xylenes. Some individual
hydrocarbons have specific regulatory limits, some have associated
guidance values, but the majority have no recognised limit. The presence of hydrocarbons in drinking water at a customers’ tap usually indicates that spilled fuel or oil has permeated the plastic pipes underground. Limit: No regulatory standard

Present naturally in many water sources and removed during water
treatment. Iron in water supplies may also be derived from the corrosion
of iron mains or customers’ galvanised iron pipes. Iron is not harmful to
health and standards are primarily set for aesthetic reasons. Under certain conditions rust sediments in the mains can be disturbed and result in ‘brown water’. This is usually cleared by flushing the water main and taps. Limit: 200µg/l

We make sure the water leaving our treatment centres is lead-free. But if it travels through lead pipes, small amounts can end up your water. There are no lead mains in our water distribution network. Lead usually comes from older pipework connecting your property to the water main or from the internal plumbing of your property.
To protect the public, there are strict regulations governing the maximum amount of lead allowed in drinking water. Expectant mothers, young children, and bottle-fed babies are considered the most vulnerable to leads health effects.
If you are concerned that your water may contain lead, we will be happy to test your tap water. To arrange a sample or to find out information about lead, please contact us. Limit: 10µg/l

Manganese is present naturally in many water sources and is typically
removed during water treatment. Occasionally disruption to water mains
can cause sediment, containing manganese, to be stirred up and cause
‘black water.’ It is not harmful to health and flushing the tap generally clears the ‘black water.’ Limit: 50µg/l

These substances are rarely present in water although trace levels have been associated with impurities from plumbing. The standards for these are generally very stringent to reflect their potential toxicity. Strict controls, monitoring and processes are in place and these substances are considered low risk. Limit: 1µg/l

A trace metal occurring widely in the environment. Rarely present in water although coatings on some taps and other plumbing fittings may contain nickel. These fittings can impart very low levels of nickel when water is left to stand in contact with them for a prolonged period. A brief period of flushing will usually remove this. Limit: 20µg/l

Present naturally in all source waters, although higher concentrations are more commonly found in agricultural areas where nitrogen-based fertilisers are used on the land. Where necessary, nitrate levels are reduced to acceptable levels by water treatment. Liaison with the Environment Agency, farmers’ groups and landowners is important when addressing issues in the short and long term. Limit: 50mg/l

Traces of nitrite may be produced when chlorine and ammonia are used
together in the disinfection process. This process is not used at our
treatment centres. Limit: 0.5 mg/l

Some colony count bacteria can show up in another test and are described by their appearance. Their significance is the same as other colony count bacteria. Limit: None specified.

Pesticides - aldrin, dieldrin, heptachlor and heptachlor epoxide. These are persistent organo-chlorine chemical compounds no longer used in the UK. Generally they are not found in water sources but a more stringent standard has been set on the basis of their toxicity. Limit: 0.03µg/l

This group includes organic chemicals with a wide range of uses such as
weedkillers, insecticides and fungicides. Many water sources contain traces of pesticide residues as a result of both agricultural and non-agricultural uses of pesticides on crops, and for weed control. Some of these chemicals persist in the environment. Where necessary, additional treatment is installed to remove pesticides. Limit: 0.1µg/l

This is the sum of all the individual pesticides detected. Limit: 0.5µg/l

PFAS are a group of chemicals that are extremely resistant to heat, grease and water making them a key component of many products such as non stick cookware and firefighting foams. Water companies are in the process of assessing and monitoring these chemicals to identify them, measure likely concentrations and assess the need for future mitigations. Limit: Guidance value 0.1µg/l

Also called hydrogen ion, this is a measure of the acidity or alkalinity of the water. Water having a pH of seven on a number scale is described as neutral. Lower values occur if the water is acidic. Waters are usually maintained at a pH slightly higher than neutral, sometimes by the addition of alkali during treatment to minimise corrosion of pipes. Limit: 6.5 - 9.5

Phosphorus naturally occurs in the environment and is a major component of fertilisers. It is not harmful to health and is often added to water at low levels to form a protective layer on the inside of lead pipes, reducing lead levels in tap water. Limit: None specified

These are subjective assessments at the time of sampling or in the laboratory, using the sensitivity of the human palate and nose to detect any discernible odours and tastes. Most treated water has no distinctive odour or taste although customers' plumbing can contribute to a range of tastes such as disinfectant, plastic or metal if water has been standing in pipework for periods of time. Limit: All samples are checked and any significant finding is investigated

In addition to the qualitative assessments described above, a proportion of treated water samples are subjected to more rigorous tests. These involve panels of assessors tasting and smelling the water under strictly controlled conditions to provide a more representative assessment. Limit: Acceptable to consumers and displaying no abnormal change

Radon is a naturally occurring radioactive gas found in small amounts in all rock and soil. It seeps out of the ground in some locations and can collect in enclosed spaces where it primarily poses a risk through inhalation. Radon may dissolve in ground water where this originates in an area usually already recognised as being at risk of Radon in air. When present at all in drinking water concentrations are generally low. Limit: 100Bq/l

These substances are rarely present in water although trace levels have been associated with impurities from plumbing. The standards for these are generally very stringent to reflect their potential toxicity. Strict controls, monitoring and processes are in place and these substances are considered low risk. Limit: 10 µg/l

Not present in source waters and not usually present in drinking water but traces may be present when certain types of domestic filter are used. Limit: No regulatory limit

Sodium is a component of common salt. It is present in seawater and brackish groundwater. Some water treatment chemicals contain it. Concentrations in drinking water are normally very low but some water softeners can significantly add to the sodium concentration. In moderation, sodium is a normal and essential part of a healthy diet, in excess, sodium can be harmful, particularly to infants but also to adults over the longer term. Limit: 200mg/l

Occurs naturally in the environment, as mineral deposits. Sulphate is not harmful to health and is not removed during treatment. Limit: 250mg/l

The temperature of surface waters varies according to the season while in groundwater it tends to remain relatively constant throughout the year. High temperatures can cause the water to taste less palatable. Limit: No regulatory limit

These solvents are not normally present in water. They may occur in low concentrations in groundwater affected by industry where they are often used as de-greasants. Where necessary, they are removed from drinking water by special treatment. The standard for the latter two compounds relates to the sum of their detectable concentrations. Limit: 3µg/l

Hardness is a natural characteristic of water. It is formed when rainwater
dissolves calcium and magnesium salts while passing through rock such as chalk. Hardness is not harmful to health although customers may notice a difference in the amount of lather from soaps – hard water lathers less than soft water. Most of our water falls in the range moderate to very hard – the only naturally soft water in the region is found in parts of Somerset. Limit: None specified

A measure, obtained by calculation, of the effective dose of radiation the
body would receive from consumption of treated water. All water sources in our region are screened periodically for radioactivity. Limit: 0.1 mSv/yr (indicative)

TOC represents the total amount of organic matter present in the water. The concentrations in water do not present any risk to health. Limit: None specified. Significant change investigated

PAHs are components of the materials which, in the past, were used to line water mains. There are four individual PAH compounds that are monitored regularly. The sum of these four is calculated and regulated by one overall standard. PAHs are not harmful to health at the levels likely to be found in water, and do not generally cause a problem in our region. Limit: 0.1 µg/l

The standard for these two compounds relates to the sum of their
detectable concentrations. These compounds are used in a range of
industries such as the food industry, dry cleaning, and chemical production.
Strict controls, monitoring and processes are in place and these substances are considered low risk. Limit: 10 µg/l

These organic substances are by-products of chlorination, occurring as chlorine reacts with organic substances in drinking water. They are not considered harmful to health at the levels found in water. Limit: 100µg/l

A radioactive isotope of hydrogen. It is not normally found in water sources. Discharge of radioactivity to the environment is closely monitored by the Environment Agency. Limit: 100Bq/l

Turbidity measures the presence of tiny particles that may make the water appear cloudy. Air bubbles can sometimes cause the water to look cloudy although air will clear from the bottom upwards if aerated water is left to stand. Limit: 4 NTU

mg/l = milligrams per litre or parts per million µg/l = micrograms per litre or parts per billion Bq/l = becquerel per litre, unit of radioactivity (equal to one disintegration or nuclear transformation per second)

Occurs naturally in the environment and foods. Traces of zinc in water are usually from customers’ galvanised iron pipework and are not of health significance. Limit: None specified