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There are different microbiological parameters which endanger health, if their concentration in drinking water is too high. Legionella, for example, are one of the most important triggers of environmental infections in all buildings. Chemical substances such as copper, nickel or lead must not be present in harmful concentrations in drinking water as well. We inform you about the most relevant parameters.
The parameter colony number at 22 °C provides information on the status of the potable water installation. It is not a direct detection of pathogens. A sudden increase can be an indication of contamination with microorganisms. Increased colony numbers can indicate contamination of the potable water after treatment or in the distribution system up to the potable water installation (e.g. poor effectiveness of treatment / disinfection, time- and material-dependent influences of the potable water installation, accidents / pipe breaks, biofilm formation, stagnation of the potable water in the distribution system).
In addition to the status information and the indication of contamination, the occurrence of potentially pathogenic microorganisms (e.g. pseudomonas, legionella) can no longer be ruled out in potable water installations with increased colony numbers at 36 °C. The risk of contamination of the potable water system with potentially pathogenic microorganisms (e.g. pseudomonas, legionella) can also be reduced.
The presence of naturally occurring Legionella in the water is independent of faecal contamination. Legionella is a natural aquatic bacterium found in groundwater, springs, rivers, lakes, wastewater as well as in damp earth and sediments. It multiplies easily in warm water. It is an indicator of the hygienic operating condition of a potable water installation. Legionella is one of the most important triggers of infections in buildings caused by environmental factors, especially hospitals, hotels, nursing homes, etc..Its preferred habitat is warm, stagnant water, e.g. in pipes and storage tanks.
Possible sources: Whirlpools, showers, dental units, water fountains, car washes, open evaporative cooling systems with cooling water systems.
Under unfavourable conditions, it can increase to an impermissible level. A significant increase in Legionella usually occurs only at water temperatures between 25 and 55°C.
Legionella usually enters the potable water installation of a building with the incoming municipal water, although in very low concentrations. At the usual temperatures of incoming municipal water (5-10°C), the probability of finding a significant number of colony-forming units is very low.
A significant increase in the propagation of P. aeruginosa indicates, among other things, possible stagnation problems in the potable water installation. Pseudomonas occurs predominantly only in cold water and is mainly responsible for the formation of biofilms. P. aeruginosa can remain in the biofilms of water-bearing systems for years and can cause systemic contamination of the potable water installation.
P. aeruginosa can also be detected in newly laid pipelines after external contamination. It is characterised by extremely low nutrient requirements and reproductive ability even at temperatures below 15°C. In principle, all waters, including potable water, can be colonised cold. Pseudomonas aeruginosa either enters a house installation system via the house service connection line or is introduced during work on the installation or into a new installation as a result of contaminated components or tools and work material.
Dead pipes and stagnation in the house installation promote propagation.
Particularly affected are cold-water pipe systems including their draw-off points. A Pseudomonas contamination represents the most problematic type of microbial contamination in cold water networks and is an indicator parameter for the overall condition of the potable water installation. If P. aeruginosa is detected in potable water, risk-minimising measures must be taken. P. aeruginosa may cause ear infections, among other things, and is of major significance as a pathogen of nosocomial infections in hospitals.
If enterococci are detected, the occurrence of other faecal pathogens must always be expected. Due to their high persistence, detection of them alone is to be regarded as an indication of a much earlier contamination.
When E. coli is detected alone or in combination with enterococci, it is more likely to be an indication of fresh contamination. Contamination of potable water installations with E. coli or enterococci occurs either by the supply of contaminated water from the public/central potable water supply (e.g. defective supply lines, flood damage) via the house service connection or via a prohibited direct connection of the potable water installation with non-potable water systems (European Union: EN 1717), e.g. in heating water, water for extinguishing fires, process water, roof drainage water.
Another possibility for contamination by E. coli or enterococci is due to unclean work (modification, repairs) on the potable water installation.
Coliform bacteria include various types of environmental and faecal bacteria. In contrast to E. coli and enterococci, their occurrence in potable water does not necessarily have a faecal origin, but may also be caused by unspecific contamination of the potable water (e.g. ingress of dirt).
The occurrence of low concentrations does not necessarily mean an external ingress, as a sudden increase in the flow rate or a reversal in the direction of the flow of potable water can result in a mobilisation of coliform bacteria from existing deposits or from biofilms. An increase of coliform bacteria in the piping system is to be expected if unsuitable piping materials are used which release nutrients into the water, the water temperature is above 20°C and/or anaerobic conditions prevail.
Many coliform bacteria are among the obligatory or facultative pathogens that may be particularly relevant to immunocompromised patients in medical establishments. With certain underlying diseases, infections caused by coliform bacteria (e.g. Enterobacter and Klebsiella) may lead to serious complications. As it is often very difficult to determine individual bacteria genera, the value for E. coli and coliforms is usually given as a common number.
Clostridium perfringens is a Gram-positive, non-motile, rod-shaped, sulphite-reducing anaerobic bacterium. It produces endospores with extreme resistance to heat, pH extremes, UV light and disinfection processes such as chlorination or ozonation. It is found in the intestines of humans and animals as part of the normal intestinal flora. Outside the intestine, bacteria can sometimes survive for a very long time, primarily in the form of their resistant spores (e.g. in soil, dust and water). The very high resistance and persistence should be an indication of the occurrence of the similarly resistant and persistent spores of faecal-borne parasites. It can also be used as an indicator of the efficiency of disinfection and the physical removal of viruses and protozoa.
Giardia is a genus of anaerobic flagellated protozoan parasites. Their life cycle alternates between a swimming trophozoite and an infective, resistant cyst. The symptoms of Giardia, which may begin to appear 2 days after infection, include violent diarrhoea, excess gas, stomach or abdominal cramps, upset stomach, and nausea. Resulting dehydration and nutritional loss may need immediate treatment. A typical infection can be slight, resolve without treatment, and last between 2–6 weeks.
Person-to-person transmission accounts for the majority of Giardia infections and is usually associated with poor hygiene and sanitation. Giardia is found on the surface of the ground, in the soil, in undercooked foods, and water along with improper cleaning of fecal material from the hands after handling infected feces. Water-borne transmission is associated with the ingestion of contaminated water.
The Centers for Disease Control and Prevention (CDC) recommends hand-washing and avoiding potentially contaminated food and untreated water. Boiling suspect water for one minute is the surest method to make water safe to drink and kill disease-causing microorganisms such as Giardia lamblia if in doubt about whether water is infected. Chemical disinfectants or filters may be used.
Cryptosporidium is a genus of apicomplexan parasitic alveolates that can cause a respiratory and gastrointestinal illness that primarily involves watery diarrhea with or without a persistent cough in both immunocompetent and immunodeficient humans. The Cryptosporidium spore phase (oocyst) can survive for lengthy periods outside a host. It can also resist many common disinfectants, notably chlorine-based disinfectants.
Many treatment plants that take raw water from rivers, lakes, and reservoirs for public drinking water production use conventional filtration technologies. Direct filtration, which is typically used to treat water with low particulate levels, includes coagulation and filtration but not sedimentation.
Cryptosporidium is highly resistant to chlorine disinfection, but with high enough concentrations and contact time, Cryptosporidium inactivation will occur with chlorine dioxide and ozone treatment. In general, the required levels of chlorine preclude the use of chlorine disinfection as a reliable method to control Cryptosporidium in drinking water. Ultraviolet light treatment at relatively low doses will inactivate Cryptosporidium. Water Research Foundation-funded research originally discovered UV's efficacy in inactivating Cryptosporidium.
One of the largest challenges in identifying outbreaks is the ability to verify the results in a laboratory. The oocytes may be seen by microscopic examination of a stool sample, but they may be confused with other objects or artifacts similar in appearance.
For the end consumer of drinking water believed to be contaminated by Cryptosporidium, the safest option is to boil all water used for drinking.
Cases of cryptosporidiosis can have different origins. Like many fecal-oral pathogens, it can also be transmitted by contaminated food or poor hygiene. Testing of water, as well as epidemiological study, are necessary to determine the sources of specific infections. Cryptosporidium typically does not cause serious illness in healthy people. It may chronically sicken some children, as well as adults exposed and immunocompromised.
In many stress situations, bacteria lose their capacity to be cultivated on artificial media while nevertheless remaining viable: They retain their cellular structure and at a later date they can resume the process of division and propagation.
This newly discovered physiological state for bacterial cells is now referred as a ‘Viable but non culturable’ state (VBNC).
It is not known exactly how the VBNC state functions. This may vary from one bacterium to another. A large number of environmental factors that act as stressors for the cells – lack of nutrients, temperature, osmotic pressure, presence of biocides, lack of oxygen, pH value, radiation – can induce the VBNC state. It has now been shown that many bacteria, including pathogenic ones such as Pseudomonas aeruginosa and Legionella pneumophila, enter a VBNC state and thereby to some extent evade the effects of inhospitable environmental conditions.
The VBNC state represents an important refuge for pathogens in the environment. The cells are morphologically smaller and their metabolic rate is very low. The uptake of nutrients, the respiration rate and the synthesis of macromolecules are all drastically slowed down. Bacteria can remain in the VBNC state for a year.
When suitable conditions prevail again, as is the case when the bacteria are ingested, the bacteria can reproduce again, i.e. they can be cultivated and can be infectious. The VBNC state is probably a survival strategy, because the lower metabolic rate makes the cells significantly less susceptible to external influences such as the effects of toxic substances.
The capacity of VBNC cells to adhere to surfaces appears to vary from species to species. However, recent studies have shown that both Legionella pneumophila as well as Pseudomonas aeruginosa in biofilms exist in the VBNC state to some extent.
Chemical substances must not be present in concentrations that are harmful to human health. Among the chemical parameters of particular interest to a potable water installation are those with a concentration which may increase in the pipeline network, including the potable water installation. For some parameters, the concentration is directly linked to materials which are or were installed or used in the potable water installations (pipelines, appliances, fittings, soldering agents, seals). The following table shows examples of these parameters with the associated limit values in accordance with the European Drinking Water Directive 98/93/EC.
Copper in piplelines means that the use of copper pipes is therefore limited to certain potable waters. With certain, mostly hard, acidic potable waters with a high content of natural organic compounds, increased copper solubility can sometimes be observed. In conjunction with longer periods of downtime, this can lead to risky concentrations of copper significantly above 2 mg/l in the water.
Increased copper solubility is generally observed in new potable water installations made of bare copper. Depending on the water quality, it may last for a few weeks to months after commissioning. Exposure to more than two milligrams of copper per litre for several weeks to several months may be detrimental to the health of newborns and infants. There is no risk to children and adults, but potable water with more than three milligrams of copper per litre is often rejected for taste reasons. If the content is more than three milligrams of copper per litre, gastric and intestinal complaints may also be expected in the short term. (Always specify as mg/l).
Exceeding the parameter value for nickel is to be expected, above all, where nickel-plated components were used or chrome-plated end fittings are present where some of the surfaces in contact with the water have nickel layers which are not covered by the chrome layer. The resulting concentrations are harmless to people of normal health of any age. However, people who are pre-sensitised to the allergenic effects of nickel – equivalent to around one-sixth of the population – may be more sensitive.
Lead is a nerve and blood toxin that can accumulate in the body and may have an detrimental effect on the development of a child's nervous system. Therefore, pregnant women, unborn babies, infants and toddlers are particularly at risk and should be protected against the ingestion of lead. Other installation materials, such as galvanised steel or copper alloys, may also release lead into potable water. The German Environmental Agency (UBA) specifies in a recommendation the materials suitable for potable water hygiene, for which it has been proven that they do not exceed the new lead limit value.
Since December 2013, a maximum limit value of 0.010 mg/l of lead in potable water has been in force in Germany. As a rule, this value cannot be met by potable water flowing through lead pipes. In combination with other metal materials, even smaller sections of lead pipes can result in high lead contents in the water. Therefore, when lead pipes are being replaced, it should be ensured that they are replaced in full. However, if lead pipes still exist, they should be replaced as soon as possible. Shut-off valves and domestic water meters made of copper alloys can also easily result in increased concentrations of lead. The zinc layer on hot-dip galvanised steel pipes is contaminated with lead during manufacturing. This can cause the potable water to be contaminated with lead, even if the potable water installation itself contains no lead pipes.
In contrast to Europe, no lead is permitted to be present in alloys in the USA.
‘Brown’ – rusty – water can be produced from older pipelines with galvanised steel after a longer period of downtime. Due to turbidity and a high iron content, such coloured water is not of a quality required by the regulations on potable water; however, it does not pose an acute health risk. However, this technical abnormality may soon pose a problem from a hygiene viewpoint and could be an indicator of a possible microbial contamination. Current pipelines made of stainless steel are suitable for all potable waters and are hygienically safe.
The concentrations of the metals lead, copper and nickel in potable water samples at the consumer's draw-off point (‘tap’) are primarily determined by the following influencing factors: