A questionnaire study and field visit showed that diazinon and malathion were the most commonly used pesticides in Qazvin province, Iran. Concentrations of these pesticides were determined in water sources; include springs, wells and Shahrood River. Springs water samples had the best water quality; but deep wells were the most polluted water samples. Diazinon was detected in 46.6 % of the samples, while malathion occurrences frequency was in 13.3 % of the samples. Diazinon and malathion were detected in maximum concentration of 19.44 and 18.12 μg L(-1), respectively. The obtained results showed that diazinon was detected in higher than life-time health advisories in wells and in Shahrood River samples; so, it can bring up threats to human health. Interpolation of diazinon and malathion in water sources showed that diazinon had the most widely scattering condition in deep wells. Also, cross validation with the root mean square error (RMSE) indicated that the natural neighbor interpolation of malathion has the minimum RMSE.