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Summary Among laboratories there is a great need for reference materials for organic components. These reference materials can be used for quality control purposes, method validation and to establish equivalency of methods. However, the availability of suitable reference materials is limited. In the framework of this project a reconstitution protocol is drawn up. The protocol describes in detail the preparation of reference materials for organic compounds in ground and surface water. To draw up a draft protocol a limited literature search was made and a survey was conducted between members of FeNeLab. The draft protocol describes in detail how to prepare synthetic ground and surface water using pro-analysis grade chemicals and ultra pure water. Both matrices are spiked with organic components with a solution from resealable ampoules. In this project dichloromethane, toluene, trichloroethylene, naphthalene, indeno(1,2,3,-cd)pyrene and mineral oil were used for spiking. The draft protocol is evaluated for practicability in an intralabortory test. The results of this test were sufficient to evaluate the robustness of the draft protocol in an interlaboratory test. However the results of the measurements are so different from each other that they could not be pooled. This may be a consequence of the fact that the participating laboratories used different analytical methods. Therefore the robustness of the protocol is separately evaluated for each laboratory. To perform the evaluation as strict as possible, the influence of the used analytical method is eliminated as much as possible. The evaluation is done using the ratio of reproducibility and repeatability. It appeared that evaluation of the robustness of the protocol can not be done without taking into account the influence of the analytical method on the recovery and the dispersion of the results of measurement. The results of the project are: The developed reconstitution protocol is robust and suitable for the preparation of reference materials of organic components in ground and surface water; The reference materials can be used for validation studies and for first and second level of quality control within one laboratory. For use in interlaboratory comparison tests no valid judgment can be made with the results obtained in this project. The applied spiking level for indeno(1,2,3-cd)pyrene of 25 ng/l is too low. Other reference materials (component and concentration) can be prepared by using ampoules of different composition. The results lead to a draft Dutch standard for the preparation of reference materials.