OCCURRENCE OF BACTERIA IN DESIGN FEATURES OF A DISTRIBUTION SYSTEM
Report No FR0487

Nov 1994

SUMMARY

I BENEFITS

These studies will provide information regarding the potential of design features of a distribution system to cause a deterioration in the microbial quality of water.

II OBJECTIVES

To carry out a scoping study to assess if selected design features of distribution systems could act as a niche for coliform and heterotrophic bacteria.

III REASONS

Many water utilities experience bacteriological failures where the source of contamination can not be identified. Distribution systems contain a variety of features which may exert an influence on the microbial quality of water by providing niches for colonisation by micro-organisms or form 'dead' volumes of water in which chlorine residuals diminish to a concentration which permits microbial growth.

IV CONCLUSIONS

1. Bacteria of sanitary significance were associated with each of the design features although their numbers and frequency of occurrence were low.

2. In service reservoirs, coliform bacteria were recovered from the sediment only and not the walls.

3. There was some evidence to suggest colonisation of surfaces by bacteria of sanitary significance.

4. The numbers of heterotrophic bacteria showed considerable variation between as well as within the same feature.

V RESUME OF CONTENTS

This final report is one of several dealing with specific topics studied as part of the FWR contract Water Quality in Distribution (Project Ref F-1702). It describes the outcome of a scoping study to investigate how certain design features of a distribution system could influence microbiological quality. Several design features were selected for investigation including service reservoirs, hydrants and closed valves as well as dead ends. Sampling protocols were developed and used to obtain samples of water and 'biofilm' from a number of distribution systems. The extent to which each of these features would influence microbial quality was assessed in terms of numbers of heterotrophic and coliform bacteria.

Copies of the Report are available from FWR, price £25.00 less 20% to FWR Members