Spatial variations in tap water isotopes across Canada: Tracing water from precipitation to distribution and assess regional water resources

Abstract

With global warming and increasing water use, tap water resources need sustainable management. We used hydrogen and oxygen isotope analyses in tap water (i.e., δ2H and δ18O values) to identify issues associated with tap water resources in Canada. We analyzed 576 summer tap samples collected from across Canada and 76 tap samples from three cities during different seasons and years. We classified the samples based on their sources: groundwater (TapGroundwater), river (TapRiver) and lake (TapLake). δ2H values in tap water correlate strongly with values predicted for local precipitation across Canada with a stronger correlation for TapGroundwater and TapRiver than for TapLake. We then constructed water balance models to predict the δ2H of surface water across Canada, and validated them against Canadian stream δ2H data. δ2H values in tap water correlate strongly with values predicted for local surface water, however, the water balance models improved the predictability only for TapRiver and TapLake and not for TapGroundwater. TapGroundwater δ2H values reflect the δ2H values of annually averaged precipitation, whereas TapRiver and TapLake δ2H values reflect post-precipitation processes. We used the δ2H residuals between the observed and predicted δ2H values to assess regional processes influencing tap water δ2H values across Canada. Regionally, snow/glacier melt contributes to all tap sources around the Rockies. Tap waters are highly evaporated across Western Canada, irrespective of their sources. In the Great Lakes and East Coast regions, tap waters are evaporated in many localities, particularly those using surface reservoirs and lakes. We propose the use of these isotopic baselines as a way forward for the monitoring of tap water resources at different scales. These isotopic baselines also have valuable applications in human forensic studies in Canada.