Legionella in drinking water installations

Preventing and combating legionella

Intensive and mechanical cleaning of your drinking water system with comprex®.

Legionella bacteria are ubiquitous in freshwater and can multiply in water-bearing systems.
Elevated concentrations may occur if there are defects in drinking water installations. Then quick action is required. This is because legionella poses a serious health risk. The rod-shaped bacteria live in the water and can cause the infectious disease legionellosis through droplet transmission.

Often, attempts are made to eliminate Legionella contamination with conventional flushing. Nevertheless, the most important measure to eliminate contamination is cleaning. With the comprex® impulse flushing process, Legionella can be sustainably combated and further contamination prevented.

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Things to know about legionella

Frequently asked questions:

Legionella is a genus of rod-shaped bacteria. The non-spore-forming bacteria living in the water move around by flagella. The best known species is Legionella pneumophilia. It can cause the infectious disease legionellosis. Legionnaires’ disease, or Legionella pneumonia, is a form of pneumonia and thus poses a serious health risk. Over 1000 deaths are reported in Germany each year.

Infection with Legionella happens mainly through inhalation of aerosols, for example during showering. Washing hands and drinking water contaminated with legionella is considered safe for healthy people with intact immune systems. Human-to-human transmission has been ruled out so far.

Warm water provides optimal growth conditions for Legionella to multiply. Ideal conditions are from 25 °C, between 25 and 45 °C they multiply the most. Water temperatures above 55 °C effectively inhibit legionella growth, and at temperatures above 60 °C the germs eventually die.

Legionella survive for minutes at temperatures between 60 °C and 70 °C, and seconds at temperatures above 70 °C.

  • Hot water production plants (water tanks and boilers)
  • Cold water lines with long downtimes at temperatures above 25 °C
  • Cold water pipes with heat effect from the outside or to thermal mixers
    Circulation lines
  • Dead lines (e.g. pipelines that have not been reconstructed, pipelines to safety valves that are too long).
  • End strands with low water removal

In most cases, contamination with legionella is detected as part of the compulsory testing in accordance with the German Drinking Water Ordinance (TrinkwV). Legionella in water can be detected using standardized sampling and analysis methods. Specialized laboratories perform sampling and analysis in accordance with the Drinking Water Ordinance.

In the case of structural, operational or procedural deficiencies in drinking water installations, the concentrations may exceed the technical measure value of the Drinking Water Ordinance. This is considered to be a special indicator parameter in drinking water installations and is below the limit for Legionella spec. at 100/100 ml.

Drinking water is basically not sterile. Legionella bacteria are ubiquitous. Only a concentration above the technical measure value of the Drinking Water Ordinance is considered critical.

Microorganisms need nutrients to multiply. These come from contamination during new construction and repair of drinking water installations. Nutrients come from, among other things:

  • unsuitable materials of the pipelines, especially seals and diaphragms
  • assembly auxiliaries that have not been rinsed out
  • Contaminated filters, water meters, booster or water softening systems.
  • inadequately secured supply lines of the drinking water

According to the generally accepted rules of technology, the cold water temperature is below 25 °C and the hot water temperature of the entire circulation is above 55 °C during regular water withdrawal when the system is operated as intended.

Problems occur when:

  • Cold water is too warm: above 25 °C, should ideally be below 20 °C
  • Hot water is too cold: below 55 °C, should ideally be 60 °C
  • Too low temperature in the hot water and circulation system, whereby the return temperature must not fall below 55 °C (5K rule).
  • Thermal insulation of the piping is insufficient: e.g. cold and hot water supply lines too close together or too close to the heating line
  • Operation not in accordance with regulations: no regular water withdrawal
  • No hydraulic balancing of the circulation line

Disinfection serves to kill and thus inactivate unwanted microorganisms. A distinction must be made between plant disinfection and drinking water disinfection.

  • During system disinfection, the drinking water installation is taken out of service. A distinction is made between chemical and thermal disinfection.
  • Only substances on the list according to §11 of the Drinking Water Ordinance may be used for drinking water disinfection. The list specifies purity and maximum concentration of these substances. They are continuously dosed into the drinking water.

Cleaning is used to remove impurities by means of processes using water with and without additives (e.g. air or solids). A distinction must be made between new installations, repairs and existing installations.

  • In the case of new installations and repairs, assembly aids and unavoidable impurities must be discharged.
  • In existing plants, deposits and biofilms form over time. They consist of organic or inorganic substances. If these affect the quality of the drinking water or the function of the system, cleaning is required.

“During thermal disinfection for legionella control as defined in DVGW Code of Practice W 551, the water temperature is set so that it exceeds 70 °C at all points in the drinking water installation for at least 3 minutes. This must be checked and documented.

Thermal disinfection can also be used to inactivate other microorganisms, e.g. Pseudomonas aeruginosa, if necessary with different temperatures and exposure times. For thermal disinfection, special safety aspects such as protection against contact and scalding must be observed.”

(Source: twin No. 05, as of April 2009)

The so-called legionella circuit is a periodically operating procedure. In this process, the hot water is heated at defined intervals. The effectiveness is questionable. The Federal Environment Agency does not consider the legionella circuit and similar systems suitable for reducing legionella concentrations.

“For chemical disinfection, disinfectants such as sodium hypochlorite, chlorine dioxide and hydrogen peroxide are used. The application concentrations for disinfection of the system are significantly higher than the concentrations permitted for disinfection of drinking water according to the Drinking Water Ordinance. The required reaction times or exposure times can be up to 24 hours.

An effective concentration of disinfectant shall be demonstrated and documented at each sampling point.” After disinfection is complete, the system must be flushed with potable water until the disinfectant is completely removed.

(Source: according to twin No. 05, as of April 2009)

Thermal disinfection is often considered the best disinfection method. This involves flushing each tap for at least 3 minutes with water heated to over 70 °C. However, the materials of the plant must be suitable for this purpose. In large buildings, objects and facilities, this form of disinfection can only be carried out in stages (in strands) (from the first to the last sampling point). However, this is usually not sufficient to effectively and permanently fall below the technical measure value for legionella.

There are static and dynamic methods for chemical disinfection. Stand disinfection has several disadvantages. In the course of the exposure time, a reaction with the substances present in the pipeline, for example in the case of impurities, leads to a constant decrease in the disinfectant concentration (depletion). The effectiveness of stand disinfection is therefore increasingly diminishing. In the case of pronounced deposits or biofilms, the disinfection has only a superficial effect. Retreat spaces and nesting possibilities of microorganisms remain despite disinfection.

“In addition, since disinfectants are strongly oxidizing substances, damage to the materials used in drinking water installations (metals, plastics and elastomers) can occur under unfavorable circumstances even after a single application.”

(Source: twin No. 05, as of April 2009)

Suspended impurities or impurities dissolved in the water can be flushed out of the drinking water installation without major difficulties. The insoluble deposits and biofilms adhering to the inner surface are problematic.

Therefore, intensive mechanical cleaning is required to remove these contaminants. Disinfection can be a complementary measure.

It is necessary to remove the particles or corrosion products by rinsing or other cleaning measures, since the disinfection almost does not reach the microorganisms embedded in them.

In any case, the most important measure to eliminate contamination is cleaning.

The comprex® impulse flushing process is an effective cleaning measure for Legionella contamination.

The comprex® impulse rinsing process cleans intensively with compressed air and water only. It is used for solid deposits and incrustations as well as microbial contamination. As experts in cleaning drinking water systems, we have been applying our comprex® process to pipelines and systems since 1997, and to drinking water installations since 2005.

Operators often report that they search a long time for an effective solution when contamination occurs. Only after various measures have not been successful is cleaning considered. Mechanical cleaning of drinking water installations is well established and, according to DVGW Code of Practice W 557, the first step in eliminating contamination.

Why should you choose us?

Do you need competent support in cleaning your systems and equipment so that you can work cleanly and efficiently again?

Let us advise you and we will be happy to convince you with a test cleaning at your site.

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