Herbicides released through agricultural activities to surface waters and drinking water systems represent a major risk to human and environmental health, as well as a cost to municipalities for removal. This study focuses on the viability of glyphosate tolerant cropping systems as an alternative to atrazine based systems, and the impact of tillage practices on the runoff pollution potential of these systems. Variable intensity field rainfall simulations were performed on 9 conventionally tilled and 9 no-tilled plots treated with atrazine and glyphosate according to label. Plots were 1 m wide and 2 m, 5 m, or 10 m in length. Runoff from plots was collected at regular time intervals during two simulated rainfall events and analysed for herbicide concentration, sediment content, and volume. Though runoff glyphosate concentrations tended to exceed atrazine concentrations, maximum glyphosate concentration in runoff was approximately 20% of the maximum contaminant limit (MCL) for glyphosate, while atrazine concentrations in runoff consistently exceeded the atrazine MCL. Atrazine concentration and loading were significantly higher in runoff from no-till plots than from conventionally tilled plots, whereas glyphosate concentration and loading were impacted by tillage treatment to a much lesser degree. These results suggest that glyphosate based weed management may represent a lower drinking water risk than atrazine based weed management, especially in no-till systems.