A multi-residue method was developed for the determination of organophosphorous pesticides and Herbicide by liquid-liquid extraction (LLE) and followed by gas chromatography-nitrogen-phosphorus detector (GC/NPD). The method was evaluated with respect to the limit of detection and quantification, linearity and accuracy (repeatability, reproducibility, recovery). The method is linear over the range 2.5-25 μg L-1 for eleven pesticides and 5-25 μg L-1 for methamidophos. Correlation coefficients were higher or equal to 0.992. The limits of detection (LODs) were between 0.67 and 2.23 μg L-1. The limits of quantification (LOQs) ranged from 2.24 and 7.45 μg L-1. Recoveries of fortified water samples in two different concentration levels with 12 organophosphorous pesticides and herbicide were over 95% in high concentration and 80% in low concentration. For repeatability, relative standard deviation (RSD%) ranged between 2.79 and 10.99%, and for reproducibility (RSD%) ranged between 1.56 and 10.36 %. The developed method is suitable for routine application in water samples in accordance with the validation data and the parameter as the high sample throughput and cost effective.