[en] Stable isotopes are increasingly being used as tracers in environmental studies. One application is to use isotopic ratios to quantitatively determine the proportional contribution of several sources to a mixture, such as the proportion of various pollution sources in a water stream. In recent decades, the dual isotope analysis (¹⁵N and ¹⁸O) of nitrate and (³⁴S and ¹⁸O) of sulphate has been widely applied to track contamination sources. A common application is to use the isotopic composition of a mixture to determine the proportions of various sources in the mixture, using mathematical mixing models. To conduct water sampling in the field, researchers need to design and plan well the activity. Site visits and mapping need to be done first to identify the problem statements of the study area. Sampling points need to be set so that they are in line with the model to be used. Sampling equipment and tools must be provided adequately so that the sampling work is carried out smoothly. This paper will elaborate standard operating procedure (SOP) of water Sampling for stable Isotope analysis in the field. (author)