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Technical and hygienic abnormalities

The following list details examples of technical deficiencies that may be potential risk factors for the occurrence of microbiological contaminants (growth, release of micro-organisms with hygienic relevance) in the cold and hot water systems of buildings:

  • Improper planning (oversizing of storage tanks and pipelines)
  • Incorrect commissioning
  • Incorrect operation
  • Stagnation – dead pipes, prohibited cross connections
  • Use of unsuitable materials and components
  • Defective system components (e.g. heat exchangers, circulation pumps)
  • Pump capacity not adapted to the piping system (hydraulics)
  • Deposits in the hot water tank or defective coatings (water quality, choice of materials)
  • Corrosion damage or heavy lime deposits in pipelines
  • Temperatures below 55°C in the hot water system (PWH)
  • Temperatures above 25°C in the cold water system (PWC)
  • Insufficient insulation of the cold and hot water pipes
  • Hygienic defects at the house connections (e.g. shower hoses, aerators)
  • No regular maintenance and inspection

Another influencing factor is the biofilm itself. For the development of the biofilm community and the number of micro organisms, there are several factors directly related to water quality and the existing technical deficiencies. The parameters which significantly influence the growth of the biofilm as well as the number of micro organisms are temperature as the primary factor – (illustration), potable water quality (water hardness), biological nutrients, DOC, stagnation/residence time (primary factor 2), materials/substances and surface structure (age of the material). Detailed literature on specialist articles and research projects is available in this respect.

Too long downtimes (regular service interruptions of more than 7 days in potable water) mean that the biofilm is too sensitive and loose, allowing large quantities of micro organisms and parts of the biofilm to be very quickly distributed in the installation during pressure surges. This results in very high CFU, Legionella and/or Pseudomonas aeruginosa values at the affected draw-off points. With sufficient flow-through, a stable biofilm is formed, which does not lead to any lasting impairment of the potable water quality.

Caution also with conversions/extensions: Sudden strong changes in the flow velocity after several years of use can lead to the destruction of biofilm in the old construction (adaptation/conditioning to shear forces/conditions – strength of the biofilm surface) and with insufficient flushing to contamination of the new pipeline section.

Even hygienic-technical problems can be triggered by biofilms:

  • Contamination of the potable water due to increased biofilm formation
  • Depletion of disinfectants and possible formation of disinfection byproducts
  • Formation of odours
  • Cause of the discolouration and turbidity of potable water
  • Biocorrosion
  • Increase of flow resistance in pipes (in connection with lime)

Considering the microbiological-hygienic aspect, along with the propagation of Legionella, the environmental bacterium Pseudomonas aeruginosa is one of the most important pathogenic germs that can also spread in potable water installations. 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. Once it has established itself, lengthy, time-consuming and costly measures are often the only way to eliminate it. Minimisation of this risk involves avoiding errors in the planning, construction, commissioning and operation of the potable water installation in compliance with the general rules of engineering. The bacteria can occur here locally or systemically in the cold and hot water area. For example, they can be found in decentralised water treatment systems such as water softeners, in systems for the production of dialysis water, in pipeline sections with stagnant water, but also in the area of extraction fittings and directly at taps (e.g. aerators, shower heads). The contamination can occur both in existing potable water installations as well as in installations where new measures or modifications have taken place before or shortly after commissioning of these systems.