The objective of the present study was to investigate the temporal trends of 46 pesticides and 8 transformation products (TPs) in the surface water of Québec and assess their associated health risks posed through drinking water consumption. Surface and drinking water were sampled twice per week at a drinking water treatment plant (DWTP) from 2021 to 2023 (838 days). Pesticide and TPs concentrations were analysed using ultra-high-performance liquid chromatography coupled with mass spectrometry. The data were used to evaluate temporal variations of pesticides and TPs at the source, their removal in DWTPs, their human exposure via drinking water, and the associated health risks. The results showed that peak concentrations of most pesticides and their TPs in surface water occurred in June and July, and some TPs (such as metolachlor ethanesulfonic acid, metolachlor oxanilic acid, and desethylatrazine) exhibited higher concentrations than their parent compounds in surface water. Post conventional treatment analysis revealed no significant decrease in the total concentrations of target pesticides and TPs in drinking water. Notably, 11 pesticides (such as atrazine, mecoprop) and 1 TP (desisopropylatrazine) showed higher concentration in drinking water than in surface water. The hazard index (HI) was up to 18 times higher in summer peak periods than the annual average. Finally, TPs exhibited HI 1.4 to 144 times higher than corresponding parent compounds. This study was the first to assess health risks of TPs versus parent pesticides in drinking water through long-term sampling, highlighting the urgent need for further TPs regulation in drinking water.