Spatial and temporal variation of drinking water quality in ten small Quebec utilities

Abstract

A comparative study relating to distributed water quality was undertaken in 10 small municipal drinking water utilities in Quebec. All of these utilities apply direct chlorination to surface water or groundwater under the direct influence of surface water without any previous treatment. These utilities were divided into two groups: four utilities that had never or rarely served water violating the provincial drinking water microbiological standards (relating to fecal and (or) total coliform bacteria) and six utilities that very often infringed upon said standards. The objective of this study was to identify key parameters responsible for the differences between the two groups of utilities, to explore the capacity of studied utilities to simultaneously and effectively handle the acute disease risk associated with microorganisms and the chronic health hazard linked to chlorination by-products and to identify the parameters upon which it may be possible to act to achieve better water quality in each of the two utility groups. The study includes comparisons of characteristics of water quality at the source, chlorination conditions in the plant, and water quality from the entrance to the extremity of the distribution system. Results show that the differences between the two groups of utilities are associated essentially with maintained chlorine residuals and heterotrophic plate count bacteria populations in corresponding distribution systems and, to a lesser extent, to the applied chlorine doses. Subsequent multivariate analyses allowed identification of variables (i.e., factors) upon which utility managers may act to improve the quality of distributed water in each group of utilities. For the group of utilities that had very little or no violation, these factors are related to disinfection levels, whereas for the group that often violated quality standards, raw water natural organic matter content reduction through source water protection and raised chlorine doses and residuals appear to be the factors that may lead to better microbiological quality of distributed water. Key words: drinking water, water quality, distribution systems, small utilities, Quebec.

Development, application, and sensitivity analysis of a water quality index for drinking water management in small systems

“…To consider such variations, DBP seasonal thresholds were modified specifically for this index application to take account of realistic seasonal objectives (Table 2). DBPs are also contaminants that have a particularly variable occurrence from location to location within the distribution system (Coulibaly and Rodriguez 2003;Summerhayes et al 2011;Uyak et al 2014). Moreover, this spatial variability can change seasonally.…”

“…Understanding the simultaneous variability of different water quality parameters at different time scales (e.g., days, months, and seasons) could help small-system operators take better decisions to improve overall water quality. In fact, various studies have shown that spatio-temporal variations of drinking water can be significant (Coulibaly and Rodriguez 2003;Al Khatib 2005;Giannoulis et al 2004) and that said variations are based mainly on the variability of source water quality (Sharp et al 2006;Ouyang et al 2006;Wei et al 2008).…”

Development of performance indicators for small Quebec drinking water utilities

“…These characteristics were considered according to a previous study bearing on the same 10 utilities (Coulibaly and Rodriguez, 2003b). The considered raw water quality variables were total organic carbon (TOC), turbidity, total coliform bacteria, heterotrophic plate count (HPC) bacteria and atypical bacteria.…”

“…Like raw water quality variables, these characteristics were taken from a previous study on the same 10 utilities (Coulibaly and Rodriguez, 2003b). Table 1 provides an overview of the spatial variation of water quality from the source (i.e.…”

Interpreting drinking water quality in the distribution system using Dempster–Shafer theory of evidence

“…Some common water quality indicators used for water distribution are turbidity, residual disinfectant, pH, nitrates, phosphates, organic compounds, total/fecal coliforms, and heterotrophic bacteria (HPC) (Coulibaly and Rodriguez, 2003;Hunsinger and Zioglio, 2002;Clark, 1994).…”