Bacterial Regrowth in Water Supplies
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report No UWRAA 4
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.