BacterialRegrowth in Water Supplies

Report No WSAA 4

December 1989

Executive Summary

The report contains the results of a two yearproject on bacterial regrowth in water supplies, funded by the Urban WaterResearch 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 theUrban 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 ninewater authorities, as well as from the experimental work in this projectindicated that the main factors responsible for bacterial regrowth in watersupplies 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 reticulationreservoirs, and

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

Mostof these factors contributed to regrowth because they increased turbidityand/or reduced disinfection efficiency.

Resultsof the experimental program also showed that:

i.                   Faecal coliform numbers decreased, whereas total coliform andheterotrophic plate count bacterial numbers increased with passage through adistribution system

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

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

iv.                Sediments in the distribution system contained levels of totalcoliforms and heterotrophic plate count bacteria 2 orders of magnitude higherthan corresponding volumes of water.

Copiesof the Report are available from WSAA, price $A30. Orders may be placed throughthe Bookshop at www.wsaa.asn.au or by email to info@wsaa.asn.au.