Trihalomethanes in drinking water from three First Nation reserves in Manitoba, Canada

Previous research indicates that the water distribution system used has a significant impact on the microbial quality of tap water sampled in First Nations reserves in Canada. This study tested tap water from homes in three First Nations reserves to compare the concentrations of four trihalomethanes and related water quality parameters between homes receiving piped water from a water treatment plant (WTP) versus homes equipped with cisterns that are filled by a water truck. Of all the samples collected across time from household taps, 75% of piped samples and 70% of cistern samples had TTHM concentrations exceeding Health Canada's maximum acceptable concentration (MAC) of 100 µg L^-1 total trihalomethanes (TTHMs) in treated water. In all communities and across sampling times, trichloromethane (CHCl₃) was the dominant trihalomethane (42-96%) followed by bromodichloromethane (CHBrCl₂) (3-37%) and dibromochloromethane (CHClBr₂) (1-18%). Tribromomethane (CHBr₃) always accounted for < 5% of TTHMs. Within each of the three First Nations reserves, the water distribution system had no significant effect on TTHM concentration at the household level. Sampling month had a significant effect on TTHM concentration due to temporal changes in dissolved organic carbon of the source water. Results suggest that families in the studied First Nations reserves receive drinking water with high TTHM concentrations and that improvements to the water treatment plant might be the most effective way to minimize trihalomethane formation.