Following several of the larger contamination incidents in drinking water supplies,
indicator organisms (coliforms, E. coli, enterococci) have been present in the
distribution network for a long time even after extensive flushing. For example E.
coli and coliforms were present in the distribution system of Aarhus for 5 to 6
weeks (2002), without the source being identified. Numerous observations
regarding the presence of indicator organisms in drinking water distribution
systems can not be explained by the current knowledge. In order to evaluate the
significance of such presence of coliforms, it is necessary to gain further
knowledge on which circumstances they can survive - or maybe even grow - in
The purpose of this project was to investigate the survival of selected indicator
organisms and pathogens in contact with different types of pipe material and in
pipes collected from distribution systems with special focus on the interaction
between water phase and biofilm. Furthermore the purpose was, to investigate the
influence of working procedures when replacing distribution pipes, including
whether renovation of pipes represents a risk for the microbial drinking water
Firstly, the working procedures during renovation work were mapped. An
assessment of the working procedures at Nordvand A/S identified a series of risks
for the microbial drinking water quality before, during and after the renovation
work. Based on the identified risks a number of recommendations for the water
supplies were prepared – including storage of new pipe preventing the inner
surfaces to get in contact with the environment, the renovation work should be
performed as controlled as possible, the staff should be trained in hygiene, defined
procedures for the renovation work etc.
Microbial analysis of the water from renovation dig-outs revealed high bacterial
counts and a significant level of indicator organisms (coliforms, E. coli,
enterococci). This water can cause problems in the distribution network if it gets in
contact with the inner surfaces of the new water pipes. Therefore the working
procedure during renovation should always include removal of water from the digouts.
This project has lead to Nordvand A/S having more structured work procedures for
pipe renovation. After the implementation of the new procedures, Nordvand A/S
has only experienced few occurrences of high bacterial counts in relation to pipe
renovation. Thus the project demonstrated that high bacterial counts following pipe
renovation can be prevented by good hygiene and standardised working
To evaluate the risk of a microbial contamination in relation with renovation work,
the survival of a number of bacteria was investigated. This work included seven
strains of Escherichia coli, seven strains of Klebsiella pneumoniae and six strains
of Campylobacter jejuni, isolated from both clinical patients and the environment.
Initial concentrations of E. coli and K. pneumoniae were 100-200 cells/ml and of
C. jejuni 1000 celler/ml, which are low concentrations close to realistic levels. All
strains of the indicators E. coli and K. pneumoniae survived for more than four weeks in drinking water, which is a relative long time considering that the
residence time of drinking water in distribution networks usually is shorter than
one week. Strains of the pathogen C. jejuni were only detected in the water phase
for two to five days by the applied analysis method. In general strains of K.
pneumoniae (T½: 11-42 days) survived better than strains of E. coli (T½: 6-18
days). All strains of K. pneumoniae and E. coli could also be detected in the
biofilm on PE-pipes, while none of the C. jejuni could be detected in biofilms.
Generally K. pneumoniae colonised the biofilm of the pipe surfaces to a higher
degree than E. coli. However, the water phase concentration of K. pneumoniae and
E. coli was always higher than the biofilm concentration. K. pneumoniae and E.
coli always decayed significantly in the water phase during the four weeks
investigated, while the biofilm concentration was relatively stable. This indicated a
better survival in the biofilm.
The survival of E. coli and K. pneumonia in drinking water was inhibited by the
presence of plastic materials (PE (polyethylene), PEX (cross-linked polyethylene)
and silicone) and the degree of the effect depended on material type. Silicone had
the strongest inhibition on the survival in the water phase followed by PE and PEX
(silicone >> PE > PEX). Both indicator organisms were detected in the biofilm on
all three materials during the four weeks investigated. Contact with plastic pipes
had no effect on the survival of C. jejuni in drinking water and C. jejuni was not
detected in biofilms on any of the materials. There was no clear distinction between
the colonisation of the biofilm on the three materials, though the biofilm density
was higher on silicone than on PE and PEX.
It was investigated how indicator organisms and pathogens survived under realistic
conditions, i.e. in pipes collected from a real distribution system, with scalings and
mature biofilms. Both indicator organisms - E. coli and K. pneumoniae – were
detected both in the water phase and in the biofilm for more than four weeks in PE
pipes, but only for two weeks in cast iron pipes. C. jejuni was detected in the pipes
for up to three days by the applied analysis method, and only in the water phase. C.
jejuni might be present in a viable-but-not-culturable state, but it is unknown
whether the cells are infectious in this state. There were significantly more bacteria
(total ATP) in the water phase of cast iron pipes than in the investigated PE pipes,
and the biofilm density on cast iron pipes was larger than on PE pipes. The older
the PE pipe was the higher was the biofilm density and the higher degree of
colonisation of the biofilm with indicator organisms.
The project has demonstrated that high bacterial counts following pipe renovation
can be prevented by good hygiene and standardised working procedures. It is
important that water from the renovation dig-outs do not get in contact with the
inner surfaces of the new water pipes, since this can affect the microbial drinking
water quality. Laboratory investigations with new and old pipes collected from real
distribution systems demonstrated that indicator organisms can colonise the
surfaces of pipes and survive for more than four weeks. Laboratory investigations
demonstrated that pipe material influenced the survival of indicator organisms and
most likely also the survival of pathogens, with indicator organisms surviving in
drinking water for two weeks in cast iron pipes and four weeks in plastic pipes (PE,
|Number of pages||80|
|Publication status||Published - 2011|