A study of bacterial populations in metropolitan Adelaide domestic reticulation pipes was conducted to investigate a possible link between copper in drinking water and biofilms. Biofilm densities from cold water copper pipes at 10 sample sites were measured by viable cell counts. The range detected was from <2 x 101 to 3.25 x 107 cfu cm-2. Five isolates were selected for further experiments as they represented a range of responses to solvated copper and relative tendency for adhesion on glass slides. Drinking water supplied to the Adelaide Hills is high in total organic carbon (TOC; 22.57 mg C l-1) and has a negative Langelier Index (LI; - 1.16); whereas Adelaide metropolitan water undergoes filtration and has both a lower TOC and LI (10.72 mg C l-1, LI, -0.49). Copper coupons were exposed to biofilm isolates (24 h), washed and resuspended in Adelaide metropolitan and Adelaide Hills water. Copper coupons not exposed to biofilm isolates were suspended in respective waters as a control. After 5 d of incubation, the copper content of Adelaide Hills water (4.71 ± 0.87 mg Cu l-1), in which the copper coupons were suspended, consistently exceeded values obtained in the metropolitan Adelaide water (1.17 ± 0.249 mg Cu l- 1). The concentration of copper in the Adelaide Hills water was influenced by the bacterial species forming the biofilm on the coupon, with Agrobacterium sp. producing significantly higher levels of soluble copper than the control. The experiments reported here indicate that the suspended organic carbon, the aggressivity of the water and the biofilm may independently or synergistically increase the dissolution of copper from pipes into drinking water.