As well as the ten key parameters, there are a number of others that are especially significant in Scotland. These are described below:
Cryptosporidium is a protozoan parasite that lives in the gut of animals and spreads by forming resistant spores (oocysts) that are excreted to infect another host. There are a number of species that infect different hosts, including humans, and can cause stomach cramps and diarrhoea. Infection can be dangerous to those without strong immune systems, although most people recover without lasting effects. The tiny size of Cryptosporidium oocysts (about 5 micrometres) means that a robust water treatment process is necessary to remove it from water supplies. Some smaller treatment works in more rural parts of Scotland may not be capable of consistently removing Cryptosporidium and it is not unusual to find it in some of these supplies, although there is little evidence of any resulting ill-health. Plans are in place to upgrade all water supplies in Scotland so that they meet a minimum treatment standard that is capable of removing Cryptosporidium. No routine monitoring of private water supplies for Cryptosporidium currently takes place, so the risk from these supplies is unknown, but likely to be significant.
There is no Regulatory standard for Cryptosporidium, so technically no failure can occur, however it should not be present in the water supply. The detection of the occasional oocyst in a supply is unlikely to be of major health concern, although it should be investigated as it could indicate problems with the water treatment process or water source. Cryptosporidium is usually reported as a number of oocysts per 10 litres of water, and where this value is significant it may be necessary to implement precautionary measures following discussions with health professionals, such as warning consumers to boil water prior to drinking and undertaking a full review of the water catchment and treatment process.
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These are a group of bacterium that live in the gut of warm blooded animals, so their presence in the water supply can indicate contamination of that supply by faecal matter.
Some species of Enterococci cause infection, so their detection in a water sample must be taken seriously and investigated. They should not be present in the water supply and immediate action must be taken if they are found.
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This bacterium is common in the environment but should be removed by the water treatment process.
Clostridium perfringens can form spores that are resistant to chlorine, so its detection in the water supply can indicate persistent contamination over a long period of time and should be investigated. It can cause illness, but this is relatively unusual.
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Nitrite is a compound of nitrogen and oxygen that forms through biological action on ammonia. It can be present at treatment works where control of a disinfection process known as chloramination is poor. It can also form in distribution systems, again where chloramination is used, if the residence time of water in the pipes is long, disinfectant residuals are low and microbiological action takes hold. The standard for Nitrite is 0.1 milligrammes per litre in water leaving the treatment works and 0.5 milligrammes per litre at consumers’ taps.
The standards for nitrite are health-based, although they are set with a wide margin of safety. Any failure should be investigated and acted upon by Scottish Water. Controlling disinfectant residuals and measures to reduce the length of time water remains in the distribution system can control nitrite formation.
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Benzo(A)Pyrene (also known as Benzo-3,4-Pyrene) is a polycyclic aromatic hydrocarbon that enters water supplies from coal tar lined water mains. It is occasionally detected at concentrations in excess of the standard. Benzo(a)pyrene has been shown to cause cancer, consequently the standard in drinking water is low at 0.01 microgrammes per litre.
Failures of the standard are rare in Scotland. Where they occur, Scottish Water is expected to inform and take advice from health professionals to ensure consumers are protected. DWQR also expects Scottish Water to investigate the failure and take immediate action to reduce concentrations. The length of main causing the problem should be identified and appropriate measures taken.
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