A liquid–liquid extraction (LLE) method was validated as per SANTE/12682/2019 guidelines for gas chromatography–mass spectrometric (GC–MS) determination of thirty-six multiclass pesticides in environmental waters. Seasonal (summer, monsoon, and winter) effects on the magnitude of pesticide residues in environmental water (river, pond, and tube well) of six different urban areas of Nadia and North 24 Parganas districts (New alluvial zone, Eastern India) was monitored for subsequent risk assessment. Total 288 water samples (96 each of river, pond, and tube-well) irrespective of locations and seasons were monitored for multiclass multi pesticide residues during the experiment. Each sample (750 mL) was extracted with ethyl acetate/dichloromethane (8:2) liquid–liquid partitioning and filtration (0.22 μm nylon filter paper) and total residue was reconstituted in acetone (1 mL) for GC–MS analysis with developed and validated method resulting satisfactory recovery percentages (77.84–118.15%). The maximum no. of organochlorine (OC) and organophosphorus (OP) pesticide residues were dominated in river and pond water irrespective of seasons and monitoring sites. About 74% of river water samples were found to be contaminated with concerned pesticides in variable magnitudes. Monsoon (July to October) season was highly alarming with the highest presence of total pesticide residues in different types of environmental waters. Risk quotient (RQ) acute and chronic was also evaluated in pond and river water as sometimes used for drinking purposes. RQ value (5900) of total endosulfan indicates the highest risk of chronic toxicity to river fishes. Seven water samples from tube-wells were also monitored and found to be contaminated with butachlor and chlorpyriphos in non-significant amounts (< 0.1 ng mL −1 ), irrespective of seasons and sites, thus safe for consumption.