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Temporal variations in concentrations of pathogenic microorganisms in surface waters are well known to be influenced by hydrometeorological events. Reasonable methods for accounting for microbial peaks in the quantification of drinking water treatment requirements need to be addressed. Here, we applied a novel method for data collection and model validation to explicitly account for weather events (rainfall, snowmelt) when concentrations of pathogens are estimated in source water. Online in situ β-d-glucuronidase activity measurements were used to trigger sequential grab sampling of source water to quantify Cryptosporidium and Giardia concentrations during rainfall and snowmelt events at an urban and an agricultural drinking water treatment plant in Quebec, Canada. We then evaluate if mixed Poisson distributions fitted to monthly sampling data ( n = 30 samples) could accurately predict daily mean concentrations during these events. We found that using the gamma distribution underestimated high Cryptosporidium and Giardia concentrations measured with routine or event-based monitoring. However, the log-normal distribution accurately predicted these high concentrations. The selection of a log-normal distribution in preference to a gamma distribution increased the annual mean concentration by less than 0.1-log but increased the upper bound of the 95% credibility interval on the annual mean by about 0.5-log. Therefore, considering parametric uncertainty in an exposure assessment is essential to account for microbial peaks in risk assessment.

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that is widely occurring in the environment and is recognized for its capacity to form or join biofilms. The present review consolidates current knowledge on P. aeruginosa ecology and its implication in healthcare facilities premise plumbing. The adaptability of P. aeruginosa and its capacity to integrate the biofilm from the faucet and the drain highlight the role premise plumbing devices can play in promoting growth and persistence. A meta‐analysis of P. aeruginosa prevalence in faucets (manual and electronic) and drains reveals the large variation in device positivity reported and suggest the high variability in the sampling approach and context as the main reason for this variation. The effects of the operating conditions that prevail within water distribution systems (disinfection, temperature, and hydraulic regime) on the persistence of P. aeruginosa are summarized. As a result from the review, recommendations for proactive control measures of water contamination by P. aeruginosa are presented. A better understanding of the ecology of P. aeruginosa and key influencing factors in premise plumbing are essential to identify culprit areas and implement effective control measures.

The applications of in vivo probes that can detect the fluorescence of cyanobacterial phycocyanin are emerging and widely used for cyanobacterial detection in source waters. The objectives of this project were to study the sources of interferences involved with the readings of five probes (three commercially available probes and two prototype probes) using laboratory cultures and field samples. To compare the direct readings of different probes, the probe readings were presented in the form of a biovolume equivalent of cyanobacteria. Inorganic turbidity and the presence of algal biomass interfered with probe readings. A correction factor was developed for the cyanobacteria probes using simultaneous chlorophyll a measurements. The field data demonstrate that the potential underestimation of cyanobacterial biomass that corresponds to alert levels is a major issue with the application of in vivo probes. These alert levels are used to trigger monitoring and management actions. This study shows that the correlation between a probe’s reading and cell count is almost meaningless, and that the correlation to biovolume is a relevant option for management purposes. Results show that probe users should be fully aware of the sources of interferences when applying and interpreting the results. In addition, the authors offer a novel procedure that corrects for chlorophyll a interference.

To assess the state of knowledge regarding the effectiveness of distribution system disinfectant residuals during accidental microbial intrusions, the authors reviewed laboratory-, pilot-, and full-scale experimental studies. The persistence of microorganisms in the biofilms of simulated mains at the laboratory scale was much longer than in pilot-scale settings, under the typical disinfectant residual concentrations used in distribution systems. Most of the studies reviewed used culture-based methods for the enumeration of microorganisms, which are known to underestimate the number and diversity of microorganisms. Because the distribution system is the last barrier between the treatment plant and the consumer, intrusion is of concern to utility managers. Conditions experienced during some repairs—zero- or low-flow conditions and/or delay in reinstatement of disinfection—are likely to be critical for the persistence of intruded microorganisms in the biofilm, a fact that underscores the importance of adequate chlorination and flushing procedures. For the research community, this review highlights the need for additional studies using methods (e.g., molecular tools) that allow the detection of viable but nonculturable microorganisms.

This study tracked changes in chlorite ion (ClO 2 -) and chlorate ion (ClO 3 -) concentrations in the distribution system of the City of Laval, Quebec, following use of chlorine dioxide (ClO 2 ) or free chlorine. Water was collected in small- and large-diameter pipes with respect to the residence time of each sampling point In the network fed by a treatment plant using ClO 2 in postdisinfection, ClO 2 - concentrations decreased with increasing water residence time. In the networks fed by treatment plants using free chlorine in postdisinfection, ClO 2 - levels remained below the method detection limit (MDL). ClO 3 - concentrations measured in the network following ClO 2 postdisinfection were found to be either below the MDL or stable at a low level (0.09 mg/L) in cold water; ClO 3 - levels decreased slightly in warm water with increasing residence time. In the networks using free chlorine as a postdisinfectant, ClO 3 - levels showed significant variations in their overall concentrations during different samplings or with specific changes in their concentration related to residence time.

The fate of disinfectants and disinfection by-products (DBPs) has been studied in laboratories under a variety of controlled, constant conditions, but limited information is available about their fate in full-scale distribution systems. A study of the City of Laval (Quebec) distribution system examined changes in the concentrations of chlorine and dissolved organic halogens (DOX) as the water flows through the distribution system. Water was collected in small- and large-diameter pipes with respect to the residence time (RT) of each sampling point. Free and total chlorine concentrations decreased with increasing RT in the distribution system. The influence of pipes on chlorine decay was particularly important in warm water; at similar RTs, chlorine concentrations were lowest in the small-diameter pipes, greater in the main pipes, and greatest in the batch incubations. The presence of corrosion by-products in pipes appeared to be the major factor influencing chlorine decay in the distribution system. DOX concentrations generally increased with increasing RT in the presence of free chlorine and decreased when free chlorine concentrations were below the method detection limit. Results pointto significant pipe influence on DOX concentrations. DOX decay seemed to be attributable to the chemical instability of some DBPs and the presence of microbial biomass.

This study's integrated approach used a diversified database, a simulation model, and a computer visualization tool to identify the main factors that could be responsible for water quality variations.

Biological activated carbon (BAC) filtration is used in drinking water treatment to biodegrade dissolved organic carbon (DOC) and to nitrify ammonia. This study evaluated BAC filters before, during, and after shutdown. Concentrations of five substrates were measured: ammonia, nitrite, nitrate, DOC, and dissolved oxygen. Media samples were taken simultaneously at similar depths to evaluate the effect of a shutdown on the densities of fixed bacteria. Dissolved oxygen concentrations quickly dropped below 2 mg/L within the BAC filters during the first 2 h of filter shutdown. At the same time, nitrite and bromide concentrations increased rapidly. Fixed bacterial biomass densities, measured at several depths in the filter after a 24-h shutdown, declined. Concentrations of DOC and ammonia, measured in the effluent after the filter was restarted, were higher than those measured before shutdown. Backwashing after shutdown, before the filter was returned to normal operation, eliminated these negative effects and restored the biodegradation performance of the BAC filters.

The effect of filter backwash on the efficiency of first-stage sand-biological activated carbon (BAC) filters was evaluated by comparing, in first-stage sand-BAC filters, concentrations of ammonia, biodegradable dissolved organic carbon, aldehydes, and oxalate. These concentrations were measured before and after filter backwash. Filter position (first-stage sand-BAC filters versus second-stage BAC filters) was also studied to understand how flocs and particle accumulation influenced the efficiency of the first-stage sand-BAC filter. A first-stage sand-anthracite filter operated under similar hydraulic conditions and effluent turbidity acted as a reference. Filter backwash improved the efficiency of sand-BAC filters, especially in cold water sources. However, both filters produced similar water quality. First-stage sand-anthracite filters did not adequately remove biodegradable organic matter and ammonia.

Empirical findings were used to evaluate a deterministic model of bacterial dynamics in a pipe carrying potable water. The SANCHO model simulates the response of fixed and free bacteria in the system to the concentrations of chlorine and organic substrate entering the system. The authors tested the model on seven fullscale distribution systems and made a study of the error distribution between measured values and the model's predicted values. Various simulation examples demonstrate the usefulness of the model for determining a bacterial regrowth control strategy for distribution systems. Coupled with residence time calculation software, the SANCHO model may become an important decision-making tool in the management of water distribution systems. The model is particularly useful in that it can help define the reduction thresholds for biodegradable dissolved organic carbon required to maintain a given network's quality objectives as a function of the residence time of the water in the system.

The influence of service lines on the microbiological quality of drinking water was investigated. The microbial water quality in domestic service lines was found to differ from that in the main pipes of the distribution system. Differences in bacterial counts from the first flush of the service line and from the main pipe were generally more pronounced in service lines located near the plant. After a thorough flushing of the service line, however, tap water quality was found to be equivalent to that in the main pipe. Bacteriological parameters studied were total direct count after acridine orange staining, heterotrophic plate counts, total coliforms, and Aeromonas. Physicochemical parameters measured included temperature, oxidant residual, and total, dissolved, and biodegradable organic carbon. Lead and copper concentrations were determined in the first flush, after flushing the service line, and in the water samples from the main pipe.