To quantify the influence of septic system effluent on streams, 294 samples from 173 stream sites in southern Ontario, Canada, were collected between 2008 and 2015 and analyzed for four artificial sweeteners, acesulfame, saccharin, cyclamate, and sucralose. These artificial sweeteners are powerful tracers of wastewater in the environment due to their widespread use in consumer products and their high concentrations in raw and treated wastewater. Septic systems are known to contribute artificial sweeteners to groundwater, which can subsequently discharge to surface waters. 91% of the stream water samples collected as part of this dataset contained one or more artificial sweeteners, indicating a contribution of groundwater that originated from septic system effluent. Detailed information on the collection and interpretation of this data is published in Journal of Hydrology X 7: 100050. https://doi.org/10.1016/j.hydroa.2020.100050.