DISINFECTION BY-PRODUCTS IN SMALL ALBERTA COMMUNITY DRINKING-WATER SUPPLIES

Abstract

Complacent attitudes toward drinking-water quality can lead to compromised disinfection practices, as noted in such episodes as Walkerton and North Battleford. The first priority for drinking-water providers must be to ensure microbial safety. However, it is recognized that effective disinfection may not be risk free. Consequently, drinking-water guidelines seek to balance the certain danger posed by microbial pathogens with the potential adverse health hazards that may arise from disinfection by-products (DBPs). Providers of drinking water in small communities often do not have the means to reduce concentrations of DBPs, compared to utilities in larger municipalities. A significant portion of Alberta's population receives drinking water from smaller scale treatment plants or from private wells. A survey of selected DBPs was conducted in 11 rural Alberta communities, with populations ranging from 60 to 2300. The objectives were to evaluate source water quality, as measured by total organic carbon, and to measure representative concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs) at a point within each distribution system as well as within each water treatment plant. During the 5-wk study, our data show: (1) averages of THM3 (chloroform, bromodichloromethane, chloro dibromomethane) concentrations often exceed 100 µg/L (Health Canada's running annual average guideline for total THMs); (2) source waters with the highest TOC concentrations (15 mg/L) had the highest average THM3 concentrations (200 µg/L); and (3) poor source water quality may necessitate using alternative disinfection options to ensure compliance with microbial and chemical drinking-water guidelines.