Bacterial Regrowth in Water Supplies

This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.

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Report No UWRAA 4

December 1989

SYNOPSIS

The report contains the results of a two year project on bacterial regrowth in water supplies, funded by the Urban Water Research Association. The project addressed the following five tasks:

i. Literature review of research on regrowth in water supplies

ii. Review of regrowth in Australia, within the nine member agencies of the Urban Water Research Association

iii. Development of a sampling scheme to study regrowth in one supply system

iv. Implementation of the sampling scheme, and

v. Interpretation of results and a status report to the industry.

Information from the literature and from the nine water authorities, as well as from the experimental work in this project indicated that the main factors responsible for bacterial regrowth in water supplies were:

i. Little or no treatment

ii. Inappropriate choice of disinfectant

iii. Water temperatures above about 17ºC

iv. Uncovered reticulation reservoirs

v. Inappropriate design and/or inappropriate maintenance of reticulation reservoirs, and

vi. Old distribution pipes with a large number of dead-ends

Most of these factors contributed to regrowth because they increased turbidity and/or reduced disinfection efficiency.

Results of the experimental program also showed that:

i. Faecal coliform numbers decreased, whereas total coliform and heterotrophic plate count bacterial numbers increased with passage through a distribution system

ii. Different total coliform methods provided relatively similar confirmed numbers, despite differences in terms of presumptive results

iii. Coliforms within distribution system waters and sediments were generally Citrobacter, Enterobacter and Klebsiella, and

iv. Sediments in the distribution system contained levels of total coliforms and heterotrophic plate count bacteria 2 orders of magnitude higher than corresponding volumes of water.

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