Drinking Water 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 microorganisms 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. | Results are compared against long term average. Any significant difference is investigated. |
| 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 Southern Water 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 optomised to minimise plumbosolvency. | 25 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 | 3.0 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 the Government’s 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 |
| Abbreviation | 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 |
