87Sr/86Sr in Canadian tap waters: Implications for water provenance and water quality vulnerability

Abstract:

Tap drinking water is important for human health. Proper management (source choosing and watershed conservation) of tap waters requires information about the water sources. Water from different sources (i.e., groundwater, surface water) does not have the same vulnerability to environmental conditions and anthropogenic activities. While hydrogen and oxygen isotopes of tap water can help trace water cycling from source to tap, strontium isotopes may provide additional information about the drivers of tap water quality. Here, we measured the ⁸⁷Sr/⁸⁶Sr ratios of ~500 tap water samples over Canada. We delineated the corresponding drainage catchment corresponding to each sample using ArcGIS. We then apply a random forest regression that integrates geological, climatic, and anthropogenic variables to predict the ⁸⁷Sr/⁸⁶Sr variability in tap water across Canada. The measured ⁸⁷Sr/⁸⁶Sr ratios of tap water sourced from surface waters (e.g., river, lake, or reservoir) are highly predictable and are controlled by the geological and climatic conditions over the catchment. For example, tap waters in coastal regions are sensitive to sea salt deposition processes while tap waters in interior Canada mostly reflect geological conditions over the catchment. Conversely, the measured ⁸⁷Sr/⁸⁶Sr ratios of the tap water sourced from groundwater (e.g., well) are not well-predicted by the surface catchment characteristics. They are best predicted by local geological variables. The result highlights how the hydrochemistry of tap waters sourced from different hydrological reservoirs are sensitive to different environmental controls. Combining oxygen, hydrogen, and strontium isotopes from tap water could provide insights into water cycling and water management issues as well as vulnerability to water quality issues.