From our experts at SimplexHealth
Most countries have standards or guidelines regarding the maximum contaminant levels in drinking water. Globally, there is an overall agreement on the science behind the setting of these standards. Mostly, they are guided by worldwide research and the standards set by the World Health Organisation. The UK government has also published a set of water quality standards for key contaminants.
It is recommended to record your water testing results and compare them to local guidelines.
- If water comes from a private water supply, then it is important to carefully maintain the supply and test it regularly.
- Should your drinking water test outside the desired values, then it is recommended to contact your local water supplier as soon as possible or investigate the reason if you use water from a private supply.
- If a problem exists, then it is always a good idea to ask a neighbour, to see if they have the same problem to see if it is specific to your house.
- Damaged pipes, internal storage tanks or piping systems can also be causes for problems and it is useful to check whether the problem arises from the mains-fed cold tap (normally the kitchen tap) or via the storage system (check the bathroom tap).
- For lead testing or when lead is found in drinking water, more information can be found in our short guide.
- For more information about common contaminants/ elements in water and their potential effects, please also click here.
For private water supplies in the UK: All private water supplies must be registered with the local council so that monitoring can take place. Most councils have a website which provides information on processes and requirements. The national regulations are enforced through the Private Water Supplies Regulations 2016, with the Private Water Supplies (England) (Amendment) Regulations 2018. The Water Industry Act 1991 defines the powers and responsibilities of local authorities in relation to private water supply. Details about the Private Supply Regulation can be found on the Drinking Water Inspectorate (DWI) website. The guidelines determine the different types of private water supply (ie. single private dwelling, small domestic supplies etc), the sampling frequency and risk assessment as well as recommended actions in the event of a failure.
UK maximum contaminant levels or guideline standards for some key contaminants (to be measured at consumers’ taps):
| Contaminant | Concentration or Value Maximum |
|---|---|
| Aluminium | 200µg/l (= 0.2mg/l or 0.2ppm) |
| Ammonium* | 0.5 mg/l |
| Arsenic | 10µg/l (= 0.01mg/l or 0.01ppm) |
| Boron | 1mg/l |
| Coliform bacteria (E.coli) | 0 (none) |
| Enterococci | 0 (none) |
| Cadmium | 5.0µg/l (= 0.005mg/l or 0.005ppm) |
| Chromium | 50µg/l (= 0.05mg/l or 0.05ppm) |
| Chloride* | 250mg/l |
| Copper | 2.0 mg/l |
| Cyanide | 50 μg/l (= 0.05mg/l or 0.05ppm) |
| Fluoride | 1.5 mg/l (= 1.5ppm) |
| Iron | 200µg/l (= 0.2mg/l or 0.2ppm) |
| Lead | 10µg/l (= 0.01mg/l or 0.01ppm) |
| Manganese | 50µg/l (= 0.05mg/l or 0.05ppm) |
| Mercury | 1.0µg/l (= 0.001 mg/l or 0.001ppm) |
| Nickel | 20µg/l (= 0.02mg/l) |
| Nitrate NO3 | 50mg/l |
| Nitrite NO2 | 0.50mg/l |
| Odour | Acceptable to consumers and no abnormal change |
| pH (Hydrogen Ion) | between 6.5 and 9.5 |
| Selenium | 10µg/l (= 0.01mg/l or 0.01ppm) |
| Sodium | 200mg/l |
| Sulfate | 250mg/l |
| Taste | Acceptable to consumers and no abnormal change |
| Turbidity | 4 NTU |
*guide value rather than standard.
Conversions: mg/l = Milligrammes per litre, ppm = parts per million, µg/l = Microgrammes per litre
Clostridium perfringens: There is a requirement in England, Wales and Scotland to test private water supplies for C. perfringens, the result should be zero. (For more detailed advice for Scotland, please click here.)
Some of the information above may vary, please check with local guidelines. More information about UK maximum contamination levels for other parameters, can be found on this website: https://www.dwi.gov.uk/consumers/learn-more-about-your-water/ (Drinking Water Standards Leaflet), this is part of the website from the British Drinking Water Inspectorate (DWI/ DEFRA).
What about non-regulatory parameters? Most governments only regulate the maximum levels for the contaminants which are being seen as harmful. Other contaminants, which may be present in water, might be a nuisance but not harmful. Please always check with your local water supplier or plumber if an unusual concentration of specific contaminant has been found – often the cause can easily be removed.
Below is some information of how to understand the test results for non-regulatory parameters:
Alkalinity:
Alkalinity is a measure of the capacity of water to neutralise acids. Alkalinity is normally caused by presence of bicarbonate salts of calcium and magnesium, and very occasionally sodium bicarbonate may contribute. Alkalinity & pH of water are very closely linked. Testing both, the pH & alkalinity of water is important, as a very low or very high pH can be an indicator for problems with water quality. This is especially the case for water in swimming pools & spas, aquariums and private water supplies. Alkalinity in water can protect against sudden changes of the pH level. Spas should have Alkalinity of 80 – 160mg/l (ppm). If the alkalinity is below 80mg/l (ppm), then the pH can suddenly change. If a pH is too low, then water can be corrosive for metal parts, ie. lead from lead pipes can leach into water or metal parts may be damaged. If the pH is too high, then a desinfectant can not work properly. If the alkalinity is too high, then it can be very difficult to adapt or change the pH of water. Should it be necessary to change the pH as well as alkalinity of water, then it is recommended to adapt the alkalinity first.
Free and Total Chlorine:
Chlorine plays an important part in ensuring that water stays clean whilst it is being delivered to the home (sanitising effect). There is no legal limit or guide value on the levels of chlorine, the levels however should be kept as low as possible whilst ensuring the quality of the water. Should you notice a smell or taste of chlorine occasionally, then this could also be due to maintenance work. Homes which are nearer to the water treatment facility may notice the presence of chlorine more.
If you find the smell unpleasant you could fill water in a jug, then put it in the fridge to cool down before consuming it as cold water loses the smell of chlorine. Always remember to throw away any unused water after 24 hours and clean the jug regularly.
Hardness:
Hardness is due to calcium and magnesium salts dissolved in the water. The Drinking Water Directive and the UK drinking water quality regulations do not specify standards for hardness, calcium or magnesium. Where water companies artificially soften water before putting it into supply, it is recommended that they maintain a minimum total hardness of 150 mg/l (as CaCO3 calcium carbonate). The classification of when water is considered soft or hard varies depending on the author. The water hardness classification according to the DWI is as follows:
Soft water: up to 100 mg/l, slightly hard: 100-150 mg/l, moderately hard: 150-200 mg/l, hard: 200-300 mg/l, very hard: >300 mg/l (ppm) (all measured as CaCO3 calcium carbonate).
Potential solution: Could easily be removed using a water softener or certain anti-scaling products can help to prevent a build up of limescale in white goods.
Total Viable Count (TVC) / Aerobic colony count:
This is a basic measurement of the total amount of microorganisms, like bacteria, yeast and mould species, in a water sample. They are naturally occurring bacteria in water and the environment and are not harmful. It is measured by leaving the sample plate at a temperature of 22°C and 37°C for 48 and 72 hours (22°C mimics the ambient water temperature and 37°C the body temperature of humans.)
–> It is a useful test for regular maintenance of most water systems. It is recommended to carry this test out regularly, this will give a baseline measurement and help identify sudden increases/changes and any potential problems early.
There is no strict regulation for an acceptable level of TVC in drinking water. The guidelines state that there should not be a high count and there should be no significant increase from an incoming water supply.
For more information about common contaminants/ elements in water and their potential effects, please also click here.
Further Free Resources: Got a question about water testing? Try our complete list of Free Water Testing Resources.
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Disclaimer: All guidelines and recommendations accurate at time of publishing. Please check current regional / local guidelines relevant to your situation. We can not be held responsible for any information published on this webpage. The limits provided are for guidance only, we do not provide compliance statements. Only opinions based upon our own personal experience or information detailed in academic journals or other publications is cited. This has been done exclusively for anyone who is interested in this subject but is not intended to replace proper analysis or professional interpretation. We cannot accept responsibility and liability of any kind which may result from the application of this information. We always recommend to consult an expert to discuss any test results or get a full recommendation on the specific subject and specific to your situation by an expert.
Please note, that we can not give specific medical or water treatment advice. The above only reflects opinions. We cannot accept responsibility and liability of any kind which may result from the application of this information. We always recommend to consult an expert to discuss any test results or get a full recommendation on the specific subject and specific to your situation by an expert.
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There are strict standards for the quality of drinking water within Europe mainly laid down in the EU Drinking Water Directive (98/83/EC). These are based on advice from the World Health Organisation (WHO).