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Technical rules & standards

The entrepreneur and any other operator of a water supply system shall ensure that, according to the drinking water directive, suitable sample collection points are available at the water supply plants. Samples must be taken according to the acknowledged rules of technology.

The technical regulations applicable to the implementation of the Legionella test are the DVGW W 551 "Drinking water heating and drinking water pipelines, technical measures for the reduction of legionella growth, planning, construction, operation and rehabilitation of drinking water installations". The legionella examination according to W 551 essentially corresponds to the systemic investigation according to § 14 section 3 TrinkwV.

The investigation is intended to provide a first estimation of the possible contamination of a system with legionellae and their extent in order to be able to carry out an assessment and, if appropriate, suitable defensive measures. In order to determine a possible contamination of the system with legionella, a preliminary examination is first to be carried out. The number of samples required is to be selected during the orientation test so that each step is recorded. In addition, a sample must be taken at the outlet of the DHW cylinder (hot water pipe) and a sample at the inlet to the DHW cylinder (circulation pipe).

It has been attempted to interpret this clear statement in such a way that "grasp" is not equal with "sample". After our practice experience, it is very useful to sample every climbing step and not to skip single climbing lines according to the motto "courage to the gap". In our opinion, each climbing strand can be the original habitat (biofilm) of legionella populations without localized contamination being suspected. Only by sampling all the climbing strings is a differentiated picture of the contamination happening in the entire pipeline system.

The possibility given by the Federal Environment Agency to omit individual climbing strata if the selected selection of risers permits a reliable statement about the untested (eg because they are similar, have the same building parts, are equally used or are hydraulically unfavorable) Is, for example, unworkable and involves liability risks in the event of damage. This is because the binding specification can only be made by hygienically competent personnel, must also be retained for future sampling (risk of confusion) and is neither clearly defined by the wording nor by the system of W 551. In the damage recovery process, every plant operator is likely to be initially suspected of having made the restriction only for reasons of cost. We therefore urge you to sample every single step.

It has been attempted to interpret this clear statement in such a way that "grasp" is not equal with "sample". After our practice experience, it is very useful to sample every climbing step and not to skip single climbing lines according to the motto "courage to the gap". In our opinion, each climbing strand can be the original habitat (biofilm) of legionella populations without localized contamination being suspected. Only by sampling all the climbing strings is a differentiated picture of the contamination happening in the entire pipeline system.

The possibility given by the Federal Environment Agency to omit individual climbing strata if the selected selection of risers permits a reliable statement about the untested (eg because they are similar, have the same building parts, are equally used or are hydraulically unfavorable) Is, for example, unworkable and involves liability risks in the event of damage. This is because the binding specification can only be made by hygienically competent personnel, must also be retained for future sampling (risk of confusion) and is neither clearly defined by the wording nor by the system of W 551. In the damage recovery process, every plant operator is likely to be initially suspected of having made the restriction only for reasons of cost. We therefore urge you to sample every single step.

If a legionella concentration above the technical measure of 100 KbE is determined during the orientative examination, the W 551 recommends a further investigation to obtain a statement about the exact extent of the contamination of the system with legionella and to allow the initiation of targeted restoration measures. The number of samples required depends on the size, extent and branching of the system. It is advisable to take additional samples from individual sampling lines (which provide evidence of possible contamination) to the sampling points according to the orientation test on each strand. The sample volume thus goes well beyond that of the investigative study. In the administrative practice of the health authorities, the ongoing investigation is presently in our perception rather a stumbling-up existence. It is not always requested; Sofar the health authorities are satisfied with follow-up examinations to the extent of an orientation study. On the other hand, the evaluation of the findings according to Table 1a of the W 551 is very relevant to practice. The legionella concentration determined here is categorized as "low" (<100 KbE), "medium" (> = 100 KbE), "high" (> 1000 KbE) ) And "extremely high" (> 10,000 KbE) contamination with different measures and deadlines to be derived. Above all, the interpretation of the legal concept "immediately" for measures to be initiated pursuant to § 16 (7) when the technical value of the measure is exceeded is very often found in practice in accordance with Table 1a of W 551. It is important to know that the experts assume that only about 10,000 KbE is in default and immediate measures such as shower bans, use of terminal legionella filters, etc. can be arranged by the health authority.