Climate change and drinking water quality: Predicting high trihalomethane occurrence in water utilities supplied by surface water

This study estimates the impact of future variations in temperature and precipitation - associated with climate change scenarios - on the probability of total Trihalomethanes (TTHM) concentrations exceeding a threshold in drinking water. 108 drinking water utilities (DWUs) located in the Province of Quebec (Canada) were selected for this study. Temperature and precipitation variations from the period 2006-2009 to three predicted periods (2010-2039, 2040-2069, and 2070-2099) were estimated using two climate models and three emission scenarios. The probability of TTHM threshold exceedances was calculated using a multilevel logistic regression model based on three variables (treatment type, temperature, and precipitation) and three hierarchical levels (TTHM samples, DWUs and source water ecosystem). Results showed a low but significant increase in the probability of TTHM threshold exceedances over time (between 1.9% and 4.7%). There was also a significant probability difference between seasons (up to 30%) and between treatment types (between 25% and 40%).