94 IKZ-HAUSTECHNIK Sonderheft Trinkwasserhygiene 2013

Despite all of the progress that has been made in the treatment of drinking water, it is a perishable foodstuff: it is not sterile, i.e. it contains low quantities of micro-or-ganisms that do not normally pose a health risk. These organisms can only pose a pos-sible risk to the user if they are able to find suitable conditions for their propaga-tion within an installation system. This is why special care is to be take when trans-porting and distributing drinking water. This duty of care as far as house installa-tion systems are concerned comprises not only the planning and construction being carried out to the latest state of the art, it especially includes an operation in accor-dance with the intended use and a regu-lar maintaining and cleaning of the sys-tem components.

There are repeatedly reports on house installation systems being contaminated with legionella bacteria, this last but not

least being initiated by the German Drin-king Water Ordinance. This bacteria are organisms that have aquatic biotopes that are low in nutrients as their natural habi-tat, where they are to be found widespread. Due to their high level of temperature to-lerance (optimum propagation at 43-45°C) for example, legionella bacteria only have an advantage in technical aquiferous sys-tems. Should they also find additional con-ducive conditions in the technical systems, there is an exponential propagation, resul-ting in concentrations that pose a health risk. The dynamics of the propagation are shown in Table 1.

Propagation of bacteriaThe propagation initially takes place

less in the free water body and more on suitable surfaces in the form of a biofilm formation. Under favourable conditions, individual bacteria initially adhere to the

surface. The next step is the propagation and excretion of slime that contains poly-saccharide and the adherence of additional bacteria, resulting in the formation of ex-tensive clusters. If the propagation conti-nues, the result is the formation of three-di-mensional slimy structures on the surface from the extensive clusters (Fig. 1). This in-cludes a bacteria colony that mainly exists independently from the situations in the flowing water, depending on the thickness of the biofilm layer, together with it also being possible that it can contain high con-centrations of legionella bacteria. Should this film become too thick or should there be a short-term change to the flow conditions in the pipe, there is a carrying off of bacteria into the free water phase. The contamination can only be detected by water tests at this stage.

Whilst in the biofilm, the bacteria are protected from disinfectants. On the one hand, this is due to the fact that the diffu-sion of the chemicals can only take place slowly within this matrix and on the other, it is due to the fact that disinfecting agents that have an oxidising effect (such as chlo-rine) are used up as a result of them reac-ting with the constituents of the biofilm. This means that high disinfecting agent concentrations are required in order to achieve a significant reduction of the bacte-ria concentrations in biofilms (Fig. 2). For this reason, special care is to be taken from a hygiene point of view, that micro-orga-nisms that are washed in to the system are unable to find any propagation-supporting conditions. The attempting to permanently prevent the washing in by using selectively effective barriers, thereby keeping a sys-tem free from legionella bacteria, has main-ly not proven to be practical in the past.

Planning requirementsFrom a hygiene point of view, it is alrea-

dy to be ensured at the planning stage that house installation systems are so designed that all of the pipe runs really are put to re-gular use and that the flows are as uniform as possible. This avoids stagnation-related changes to the water quality. In connec- tion with this, the stagnation areas in- clude cavities (dead spaces) through which no water flows in fittings, valves, connection points or other components, from which a contamination of the piping can take place, they also normally being difficult to access when disinfecting.

The materials that are used for the cre-ating of the house installation system are not to provide nutrients for micro-orga-

Successfully avoid Microbiological ProblemsCauses – procedure in the event of a contamination – rehabilitation measures

Nowadays, drinking water in Germany is one of the best protected and controlled food-stuffs. Drinking water hygiene impairments nevertheless occur in household instal-lations now and again. The drinking water system can normally only be reused in a contamination-free state if the causes are known and suitable measures are adopted in order to solve the problem.

Sonderheft Trinkwasserhygiene 2013 IKZ-HAUSTECHNIK 95

nisms. The ultimate aim when planning and installing house installations has to be the creation of stable systems that with their technical equipment alone, minimi-se the settlement possibilities for micro- organisms. Experience gained from many objects has shown that it is also possible to equip large buildings in such a way that they can be operated in a safe manner with regard to the hygiene, as long as the exis- ting technical set of rules is adhered to. In order to ensure this however, the opera-tor needs to be instructed to a greater ex-tent on the risk of legionella bacteria and pseudomonas in buildings or house instal-lation systems that are not used in accor-dance with the intended use and on the possible procedural measures (obligation to inform!).

During the planning and construction phase, it is to be ensured that the cold wa-ter in the building is unable to heat up (ade-quate insulation of the piping or a separate

piping guide). It is also the case in the buil-ding periphery that cold water tempera-tures of 25°C (better 20°C) are not excee-ded. Vice versa, the hot water circulation in the flow should not fall below a tempera-ture of 60°C at the most remote point even during a peak decrease and in the circulati-on backflow, it should not be more than 5°C lower than in the flow. This enables tempe-ratures to be avoided in both of the drin-king water systems that could be beneficial for the propagation of micro-organisms.

Precautionary measuresEven if conditions should exist in the

existing house installation system that sup-port the propagation of legionella bacteria and pseudomonas, a targeted regular ex-changing of the water normally suffices for the keeping of the organism propagati-on in water to a minimum. Basically spea-king, the avoidance of stagnations in the drinking water system is of the highest im-

portance. Tapping points that are seldom used are also to be stated in this connec-tion (Fig. 3).

This also includes the ensuring that newly erected or converted drinking wa-ter systems are kept dry until shortly be-fore they are taken into operation and that leak tests are carried out using inert gases. As soon as the system has been filled with water, it is absolutely necessary from a hy-giene point of view that a use in accordance with the intended purpose is carried out. This means that water is to be consumed, if necessary with regular rinsing, in order to simulate a use. Just a few weeks of sta-gnation between the filling and the com-mencement of the use of a house installa-tion in a new building could suffice for the settlement of pseudomonas for example, in a system sustainably and stubbornly. The consequence of is the necessity of expen-sive and tedious rehabilitation measures and use restrictions.

Tabelle 1: Exponentielle Vermehrung bei Bakterien in einem Zeitraum von 48 Stunden.

Zeit (h) Bakterien-Zahl

0 20 1 n

2 21 2 nn

4 22 4 nnnn

6 23 8 nnnnnnnn

8 24 16 nnnnnnnnnnnnnnnn

10 25 32 nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn

12 26 64 nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn

14 27 128 nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn

... ... ... ...

48 224 16 777 216 ~ 17 Millionen

Bild 1: Bildung von Biofilmen in einem mit Trinkwasser durchströmten Schlauch (REM-Aufnahmen, 2000-fach vergrößert).

Anheftung einzelner Zellen. Bildung flächiger Cluster. Aufwuchs mehrschichtiger dreidimensionaler Strukturen.

96 IKZ-HAUSTECHNIK Sonderheft Trinkwasserhygiene 2013

A responsible ope-

rator should under all circumstances place value on the regular taking of samples by an accredited laboratory that is also appro-ved for the testing of drinking water.

Procedure in case of contaminationShould house installation system con-

tamination be detected, the first step is al-ways to be the conducting of a risk analy-sis on the part of the user: how high are the concentrations, are there risk groups among the users (e.g. older persons, per-sons suffering from a weak immune sys-tem)? If it should not be possible to reme-

dy the contamination without delay (with hot water rinsing for example), the tapping points should initially be fitted with termi-nal filters after a corresponding risk ana-

lysis has been performed, so that the user is safe for the duration of the rehabilitati-on measures.

The actual rehabilitation work should be preceded by an inspection of the tech-nical equipment and an adaptation in kee-ping with the state of the art if necessary: as long as the technical situation in the sys-tem (temperature situation, flow velocities, components) enable a bacterial propagati-on, all of the rehabilitation work can only provide a temporary respite! The “prophy-lactic“ installation of a disinfection system in a permanent operation without making any changes to the technology is not ex-pedient from a hygiene point of view: on the one hand, the permanent disinfection does not remedy the technical and hygiene deficiencies, it merely conceals them, tap-ping points that are not used or are only seldomly used are not to be impinged with disinfecting agents and on the other, it is to be taken into account that a permanent

Bild 3: Austreten von Ablagerungen und hohen Legionellen-Konzentrationen aus einer sel-ten genutzten Warmwasser-Zapfstelle (Zulauf einer Gebärwanne).

Bild 2: Desinfektion eines Biofilms mit

Natrium-Hypochlorit. Um die Bakterien-

konzentrationen signifikant zu senken, sind hohe Desinfekti-onsmittelkonzentrati-

onen nötig.

Tabelle 2: Vor- und Nachteile verschiedener Sanierungsverfahren in Hausinstallationen.

Vorteile NachteileThermische Verfahren (Heißwasserspülungen mit T. > 60 °C)

— Sofortmaßnahme—  keine chemischen

Zusatzstoffe

— Verbrühungsgefahr—  Personal- und Zeitaufwand— Kalkablagerungen—  „Totstränge“ werden nicht

erfasstChemische Verfahren (Chlorpräparate, H2O2)

—  keine thermische Belastung der Installation

—  ggfs. Rohrreinigungseffekt

— keine Sofortmaßnahme—  Beeinträchtigung des Rohr-

materials (Lochkorrosion)—  Temperaturabsenkung not-

wendig (Ausgasung)—  chemische Nebenreaktionen

(z. B. CKW)—  Desinfektionsmittelzehrung

bei hohem DOC—  „Totstränge“ werden

nicht erfasst—  gründliches Nachspülen

erforderlichTechnische MaßnahmenUmbau der TWEA und Instal-lationen (z. B. gemäß DVGW W 551), Entfernung von „Totsträn-gen“, MAG‘s

—  Dauerhafte hygienische und rechtliche Sicherheit (Stand der Technik)

—  Zusätzlich oft Energie- und Wassereinsparung

— keine Sofortmaßnahme—  zeit-, personal- und ein-

malig kostenintensiv

Physikalische Verfahrenz. B. UV-Anlagen (für punktu-elle Desinfektionen), endstän-dige Filter für die Dauer von Sa-nierungsmaßnahmen

—  effektives Verfahren ohne Nebenprodukte

—  breites Wirkungsspektrum

—  punktuelles Desinfektions-verfahren

—  kein zurückbleibender Effekt im Verteilungssystem

—  endständige Filter auf Dauer kostenintensiv

Mechanische Verfahren (z. B. Luft-Wasser-Spülungen)

—  keine thermische und chemische Belastung der Installation

— Rohrreinigungseffekt

—  kein zurückbleibender Effekt— zeitintensiv

Sonderheft Trinkwasserhygiene 2013 IKZ-HAUSTECHNIK 97

administration of disinfecting agents with adherence to the limit values specified in the TrinkwV would most probably be used up by existing biofilms in a contaminated

system, before it reaches the tap, it there-fore being rendered ineffective. The disin-fecting agents and procedures that are ap-proved in the Federal Republic of Germa-ny are to be found in the “List of Treatment Substance and Disinfection Procedures in accordance with §11 of the Drinking Water Ordinance 2001“ that has been compiled by the German Federal Environment Agency.

RehabilitationThe following aims are to be pursued

when carrying out a technical rehabilita-tion of a house installation: the water both hot and cold water) is to flow as uniform-ly as possible in all of the pipes; pipe runs or cavities (including such in fittings or other installations) in which water is not exchanged for a longer duration, are to be avoided or dismantled. The water tempe-ratures that are recommended in the tech-nical set of rules are to be permanently adhered to, i.e. cold water <25°C (better <20°C), hot water ≥ 60°C. In connection with this, not only the complex installa-tions in the house installation and the in-sulation in the diverse water systems are

to be inspected and optimised if necessa-ry or even dismantled, this is also especial-ly the case with regard to diaphragm ex-pansion vessels, drain pipes and pipe runs that are no longer used or which are used other than planned.

After completion of the technical reha-bilitation, the system is to be rinsed tho-roughly, possibly supported by deposit re-moving chemicals or physical procedures (Table 2). A disinfection could also be necessary, depending on the extent of the contamination, in order to restore a “clean” initial condition. When only dis- infection is carried out, it is to be taken into account that the dead bacteria within the biofilms still exist on the walls of the pipe (Fig. 4), these being an ideal nutritional basis for bacteria that are washed in later. In this case, a thorough rinsing of the sys-tem after completion of the disinfection is always necessary, in order to remove any disinfectant residue in addition to any de-posits that might have been removed. The success of the measures is to be validated using microbiological tests.

Should technical measures be unsuc-cessful or not be possible to the hygienical-ly required extent, it is to checked whether an improvement can be achieved with orga-nisational measures (e.g. regular compul-sory consumption with short rinsing). Fur-thermore, additional tests test should also be carried out in order to attempt to restrict the problem to certain components or run sections, enabling these to be subjected to their own treatment (Table 3). In connec-tion with this, it could be helpful if a spe-cialist for hospital hygiene or a correspon-dingly qualified microbiologist were to be consulted. ■

Authors: Dr. Christoph Koch, Dr. Stefan Pleischl

Bild 4: Unterschied chemische Desin-

fektion und mecha-nische Reinigung

eines kontaminierten Silikonschlauchs, in

dem sich ein Biofilm angelagert hat.

Bild 5: Austritt eines Biofilmpfropfes aus einem Trinkwasserzapfhahn.

–  Planung und Neubau nach dem Stand der Technik.–  Dichtheitsprüfung mit Inertgasen; Fluten so kurz vor Inbetriebnahme wie möglich.–  Bestimmungsgemäßer Betrieb; ggfs. Verbrauch simulieren, ungenutzte Zapfstellen zu-

rückbauen.–  Boilervolumina klein halten, ggfs. Nacherwärmer für Spitzenabnahme.–  Temperaturen ständig halten (Kaltwasser < 20 °C, Warmwasser ≥ 60 °C).–  Totstränge (z. B. Entleerungsleitungen) vermeiden/zurückbauen bzw. so kurz wie möglich

halten (< 3 l).–  Verteilerbalken und Boiler regelmäßig entschlämmen.–  Funktionskontrolle Zirkulation/hydraulischer Abgleich der Teilstränge.–  Löschwasseranschlüsse nur trocken oder über freien Auslauf/Zisterne.

Tabelle 3: Maßnahmen zur Vermeidung mikrobiologischer Kontaminationen in Trinkwasserinstal-lationssystemen.

Innere Oberfläche nach Desinfektion mit Chlor.

Innere Oberfläche eines kontaminierten Silikon-schlauchs nach mechanischer Reinigung.