Your water

Our scientists have tested for more than 100 substances in samples taken from household taps, 90 water treatment works and 202 service reservoirs. 

Drinking water quality standards

Our scientists have tested for more than 100 substances in samples taken from household taps, 90 water treatment works and 202 service reservoirs. 

Drinking water quality standards
Parameters tested in the UK What it means Amount allowed (PCV)
Hydrogen ion (pH) This is the measure of the acidity or alkalinity of water.  6.5 – 10.0 pH units
Colour This is an aesthetic requirement - water should be clear and bright, but may occasionally show a slight reddish or yellowish tint caused by iron from iron mains. This is not harmful to health. A common cause of discolouration is corrosion of iron mains. Programmes of work are in place to replace corroded mains. 20 mg/l Pt/Co
Turbidity Sometimes water appears milky because of air bubbles. This is not harmful and if the water is left to stand for a few minutes it will clear from the bottom upwards. A more stringent limit is set at treatment works to ensure the process is operating effectively. 1 Formazin turbidity  units (at treatment works)
4 Formazin turbidity units (at customer taps)

Dilution odour

Dilution taste

These are quality control tests to measure the level of odour and taste and are carried out by specialist testing panels. Dilution number 3 at 
25 °C
Conductivity By passing an electric current through water, water companies can measure the level of mineral salts it contains. 2500 µS/cm at 
20 °C
Residual Free Chlorine  Chlorine is added to water to remove any bacteria and other micro-organisms present in the raw water. Some remains as residual free chlorine to maintain wholesome water as it passes through the system and to the tap. We aim to keep levels at customers taps low to minimise associated taste and odour. 2500 µS/cm at 
20 °C
Coliform bacteria
Escherichia coli
Clostridium perfringens
Enterococci
These are bacteria which can be found sometimes in untreated raw water. Disinfection during treatment removes them. However, they may sometimes appear in tests in small numbers, although follow-up tests usually show that the mains water is satisfactory. Their presence in samples triggers immediate investigative work.

0/100 ml
0/100 ml
0/100 ml

0/100 ml

Colony count
2 day at 37°C
Colony count
3 day at 22°C 
Small amounts of harmless bacteria can be present in treated water. Water companies check the numbers of these bacteria. The information obtained helps to maintain the efficiency of the water treatment process and the cleanliness of the water mains. Results compared against a long term average. Any significant difference is investigated.
Ammonium Ammonium occurs naturally in water from some sources. It does not cause health problems and where it occurs, it can be controlled or removed by treatment.  0.5 mg/l

Nitrite

Nitrate

Both these substances are found in water running over and through agricultural land. Concentrations in the raw water above the amount allowed are reduced by treatment or blending. 

0.1 Mg/l at treatment works
0.5 mg/l at customers’ taps

50 mg/l 

Chloride Comes from the rocks through which the water passed but also comes from the use of salt to de-ice roads or from seawater intrusion into underground sources. It is not harmful to health.  250 mg/l

Fluoride

Fluoride occurs naturally at varying levels. Some companies add fluoride at the request of local health authorities. None of the water supplied by us is artificially fluoridated. 1.5 mg/l 
Sulphate This occurs naturally in water and comes from mineral deposits.  250mg/l 

Manganese 

Manganese occurs naturally in water and is not harmful to health.  50  µg/l 
Aluminium Aluminium occurs naturally in water and is also used to remove impurities from water in some water treatment works. Its use in water treatment is very closely controlled and continually monitored.  200  µg/l 
Acrylamide
Epichlorohydrin
These can arise from use of use of water treatment chemicals. Strict control is placed on the products we use to prevent this happening.   0.01 µg/l
0.01 µg/l 
Vinyl chloride This can be found in PVC plastic pipes after manufacture. Strict control is placed on the product we use to prevent this happening.  0.50 µg/l 
Total indicative dose
Tritium  
Measured for assessing radioactivity resulting from natural or artificial radionuclides in the environment.   0.10 mSv/year
100 Bq/l 
Sodium  Sodium salts occur naturally in water but can be added to drinking water by water softeners if these are not installed properly. Sodium at levels around 200mg/l will cause a salty taste in the water.   200 mg/l 
Copper  Traces of this metal usually come from property pipework, especially when newly installed. So called “blue water” events caused by problems with copper will be avoided through good practice in plumbing installation.   2.0 mg/l 
Iron   Iron is found naturally in some underground water. At sources where natural iron levels are high, treatment plants are provided to remove it. The use of iron in water treatment is closely controlled. It does not cause health problems. Iron is mostly found in samples taken from corroded iron mains and pipework.   200 µg/l 
Lead  Lead was formerly used as plumbing pipe material. Lead in amounts well above the standard can be a health risk if consistently consumed over many years. Water (especially soft water) passing through lead pipes can dissolve lead (plumbosolvency). Treatment is optimised to minimise plumbosolvency.   10 µg/l 
Antimony
Arsenic
Boron
Cadmium
Chromium
Cyanide
Mercury
Nickel
Selenium  
These substances are rarely found in drinking water.  5 µg/l
10 µg/l
1.0 mg/l
5 µg/l
50 µg/l
50 µg/l
1 µg/l
20 µg/l
10 µg/l 
Trihalomethanes  Trihalomethanes (THMs) derive from the combination of chlorine with organic matter. Treatment is carefully controlled to limit formation of trihalomethanes.   100 µg/l 
Carbon Tetrachloride
Sum of Trichloroethene +
Tetrachloroethene
Benzene
1,2 Dichloroethane 
These are solvents which can arise from industrial processes but can be removed during treatment. Water companies work with the industries themselves to ensure they do not reach the water supply in the first place   3 µg/l

10 µg/l

1.0 µg/l

3.0 µg/l 
Total Polyaromatic Hydrocarbons   PAHs are wide spread in the environment and have been detected in food, air and water.  They can arise in very low levels from old coal tar or bitumen lined pipes. These are no longer used but some remain in the system.   0.10 µg/l
Benzo 3, 4 Pyrene A PAH 0.010 µg/l 

Aldrin
Dieldrin
Heptachlor
Heptachlor epoxide

Other Individual Pesticides

Total Pesticides 
Water companies test for various pesticides which may be used in their areas and may be present in water. These come from their use by farmers, local authorities, gardeners etc. The traces found are no threat to health, being far lower than the limits which government medical advisers say would be necessary to protect health, but water companies are nevertheless taking steps to remove even these minute traces.  

0.03 µg/l
0.03 µg/l
0.03 µg/l
0.03 µg/l
 

0.10  µg/l

 

0.50  µg/l 
Bromate  Bromate can be formed during water treatment where ozone is used in the process. It can also arise from the use of hypochlorite when this is used as a disinfectant treatment chemical. Strict control is placed on specification of hypochlorite used in water treatment and ozonation is carefully controlled to limit bromate in treated water.   10 ug/l 
Cryptosporidium  This is a microscopic parasite that is present in the environment. We monitor water supplies where there is a risk that the organism could be found in the raw water. Low numbers are occasionally found at works but these are well below the regulatory limit.   Only measured at the treatment works 

 

Abbreviations What it means
PCV Prescribed concentration or value
< Less than
> Greater than
N/A Not applicable *
THMs Trihalomethanes
PCB Polychlorinated biphenyls
PAHs Polycyclic aromatic hydrocarbons
2d @ 37° C 2 days at 37 degrees Celsius
3d @ 22° C 3 days at 22 degrees Celsius
µsie/cm Microsiemens / centimetre
Diln.No. Dilution number at 25 degrees celsius
FTU Formazin turbidity units
deg C Degrees Celsius
mg/l Milligrammes / litre
µg/l Microgrammes / litre
ml millilitre
 
 
 
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