title: Biological instability in a chlorinated drinking water distribution network.
abstract: The purpose of a drinking water distribution system is to deliver drinking water to the consumer, preferably with the same quality as when it left the treatment plant. In this context, the maintenance of good microbiological quality is often referred to as biological stability, and the addition of sufficient chlorine residuals is regarded as one way to achieve this. The full-scale drinking water distribution system of Riga (Latvia) was investigated with respect to biological stability in chlorinated drinking water. Flow cytometric (FCM) intact cell concentrations, intracellular adenosine tri-phosphate (ATP), heterotrophic plate counts and residual chlorine measurements were performed to evaluate the drinking water quality and stability at 49 sampling points throughout the distribution network. Cell viability methods were compared and the importance of extracellular ATP measurements was examined as well. FCM intact cell concentrations varied from 5×10(3) cells mL(-1) to 4.66×10(5) cells mL(-1) in the network. While this parameter did not exceed 2.1×10(4) cells mL(-1) in the effluent from any water treatment plant, 50% of all the network samples contained more than 1.06×10(5) cells mL(-1). This indisputably demonstrates biological instability in this particular drinking water distribution system, which was ascribed to a loss of disinfectant residuals and concomitant bacterial growth. The study highlights the potential of using cultivation-independent methods for the assessment of chlorinated water samples. In addition, it underlines the complexity of full-scale drinking water distribution systems, and the resulting challenges to establish the causes of biological instability.
authors.affiliation: Department of Water Engineering and Technology, Riga Technical University, Riga, Latvia; Department of Environmental Microbiology, Eawag, Swiss Federal Institute for Aquatic Science and Technology, Dübendorf, Switzerland.
authors.forename: Alina
authors.initials: A
authors.lastname: Nescerecka
authors.affiliation: Department of Water Engineering and Technology, Riga Technical University, Riga, Latvia.
authors.forename: Janis
authors.initials: J
authors.lastname: Rubulis
authors.affiliation: Department of Environmental Microbiology, Eawag, Swiss Federal Institute for Aquatic Science and Technology, Dübendorf, Switzerland.
authors.forename: Marius
authors.initials: M
authors.lastname: Vital
authors.affiliation: Department of Water Engineering and Technology, Riga Technical University, Riga, Latvia.
authors.forename: Talis
authors.initials: T
authors.lastname: Juhna
authors.affiliation: Department of Environmental Microbiology, Eawag, Swiss Federal Institute for Aquatic Science and Technology, Dübendorf, Switzerland.
authors.forename: Frederik
authors.initials: F
authors.lastname: Hammes
mesh_terms: D060766:Drinking Water / Q000382:microbiology* / Q000592:standards; D005434:Flow Cytometry; D007844:Latvia; D014871:Water Microbiology; D018508:Water Purification / Q000379:methods / Q000592:standards; D060753:Water Quality; D014881:Water Supply / Q000592:standards*
chemical_list: D060766:Drinking Water