title: Flow cytometry for immediate follow-up of drinking water networks after maintenance.
abstract: Drinking water networks need maintenance every once in a while, either planned interventions or emergency repairs. When this involves opening of the water pipes, precautionary measures need to be taken to avoid contamination of the drinking water at all time. Drinking water suppliers routinely apply plating for faecal indicator organisms as quality control in such a situation. However, this takes at least 21 h of waiting time, which can be crucial when dealing with major supply pipes. A combination of flow cytometric (FCM) bacterial cell counts with FCM fingerprinting techniques is proposed in this study as a fast and sensitive additional technique. In three full scale situations, major supply pipes with 400-1050 mm diameter were emptied for maintenance, shock-chlorinated and flushed with large amounts of clean drinking water before taking back in operation. FCM measurements of the discharged flushing water revealed fast lowering and stabilizing bacterial concentrations once flushing is initiated. Immediate comparison with clean reference drinking water used for flushing was done, and the moment when both waters had similar bacterial concentrations was considered as the endpoint of the necessary flushing works. This was usually after 2-4 h of flushing. FCM fingerprinting, based on both bacteria and FCM background, was used as additional method to verify how similar flushing and reference samples were and yielded similar results. The FCM approved samples were several hours later approved as well by the drinking water supplier after plating and incubation for total Coliforms and Enterococci. These were used as decisive control to set the pipes back in operation. FCM proved to be a more conservative test than plating, yet it yielded immediate results. Application of these FCM methods can therefore avoid long unnecessary waiting times and large drinking water losses.
authors.affiliation: Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
authors.forename: Sam
authors.initials: S
authors.lastname: Van Nevel
authors.affiliation: Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Buysschaert
authors.affiliation: Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium.
authors.forename: Karen
authors.initials: K
authors.lastname: De Roy
authors.affiliation: Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium; Engineering TMVW (FARYS), Stropstraat 1, B-9000 Gent, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: De Gusseme
authors.affiliation: Department of Applied Mathematics, Computer Science and Statistics, Ghent University, Krijgslaan 281 S9, B-9000 Gent, Belgium.
authors.forename: Lieven
authors.initials: L
authors.lastname: Clement
authors.affiliation: Center for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, B-9000 Gent, Belgium. Electronic address: Nico.Boon@UGent.be.
authors.forename: Nico
authors.initials: N
authors.lastname: Boon
mesh_terms: D060766:Drinking Water / Q000382:microbiology*; D005434:Flow Cytometry; D005500:Follow-Up Studies; D014871:Water Microbiology; D014881:Water Supply
chemical_list: D060766:Drinking Water
keywords: Bacteria; Drinking water; Drinking water network; Flow cytometry; Urban water