Co-development of a risk assessment tool for use in First Nations water supply systems: A key step to water safety plan implementation

A review of long-term change in surface water natural organic matter concentration in the northern hemisphere and the implications for drinking water treatment

Reduced atmospheric acid deposition has given rise to recovery from acidification - defined as increasing pH, acid neutralization capacity (ANC), or alkalinity in surface waters. Strong evidence of recovery has been reported across North America and Europe, driving chemical responses. The primary chemical responses identified in this review were increasing concentration and changing character of natural organic matter (NOM) towards predominantly hydrophobic nature. The concentration of NOM also influenced trace metal cycling as many browning surface waters also reported increases in Fe and Al. Further, climate change and other factors (e.g., changing land use) act in concert with reductions in atmospheric deposition to contribute to widespread browning and will have a more pronounced effect as deposition stabilizes. The observed water quality trends have presented challenges for drinking water treatment (e.g., increased chemical dosing, poor filter operations, formation of disinfection by-products) and many facilities may be under designed as a result. This comprehensive review has identified key research areas to be addressed, including 1) a need for comprehensive monitoring programs (e.g., larger timescales; consistency in measurements) to assess climate change impacts on recovery responses and NOM dynamics, and 2) a better understanding of drinking water treatment vulnerabilities and the transition towards robust treatment technologies and solutions that can adapt to climate change and other drivers of changing water quality.

Comparing quantitative probability of occurrence to a risk matrix approach: A study of chlorine residual data

Implementation of water safety planning methods globally has focused primarily on developing an evidence base to demonstrate the benefits of the WSP methodology for risk management in water systems. However, little work has been completed to understand the appropriateness of the risk matrix method currently used to capture levels of risk for system-specific hazardous events. This study examines two quantitative risk calculations (probability density functions and event trees) compared to the risk matrix method employed in water safety planning. This analysis was undertaken to understand if the risk matrix provides an accurate estimation of risk in a water system. Two data sets were collected from nine water supply systems, both continuous inline monitoring and grab samples collected in water distribution systems (discrete events) for chlorine residual data. Using quantitative risk calculations, our study found the risk matrix does not accurately estimate risk compared to water quality data from a water system. In thirty-four (77%) of the forty-four possible scenarios investigated, the risk matrix method provided an underestimation or overestimation compared to the probability calculated using water quality data. The probabilities calculated using continuous data and the event tree method provided the closest estimations to the risk matrix, indicating larger data sets with simpler methods may be more likely to match WSP results. The lack of accuracy obtained reveals the need for a re-evaluation of the risk matrix within a water safety plan (WSP), particularly for systems with data available to perform advanced risk analysis. The risk matrix method has been used historically for systems with little data; however, for water systems with advanced water quality monitoring, adding quantitative probability calculations to a water safety plan has the potential to increase accuracy of risk assessment in water safety planning.