With global warming and increasing water use, tap water resources need sustainable management. We used hydrogen and oxygen isotope measurements (𝛿2H and 𝛿18O) 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 in tap water correlates 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 it against Canadian river water 𝛿2H data. 𝛿2H in tap water correlates strongly with values predicted for surface water across Canada with a stronger correlation for TapRiver and TapLake than for TapGroundwater. TapGroundwater 𝛿2H values reflect the 𝛿2H 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. This study provides baselines for isotopic monitoring of tap water resources and forensic studies in Canada.