This document is drafted to describe the conditions for performing, validating and safeguarding non-target screening of small organic compounds in water (drinking water, ground water, surface water, waste water) by chromatographic separation techniques with by mass spectrometry. This document can be applied to both liquid chromatography with high resolution mass spectrometry and gas chromatography with mass spectrometry. Both high and low resolution mass spectrometry can be applied, sometimes with some specific rules depending on the technique used with gas chromatography. The document is divided in three parts. The first part gives fundamental aspects in the use of chromatography in combination with mass spectrometry for non-target screening of small organic compounds in water. The second part gives the ultimate working procedure of non-target screening with liquid chromatography with high resolution mass spectrometry. The third part gives ultimate working procedure of non-target screening with gas chromatography with mass spectrometry. The second and third parts of this document refer to the reader to these guidelines for the basic principles of the method and for the configuration of the instruments. (Resolution 446 (Rovaniemi-26/2023: The first and second part of this document are submitted as NWIP. Part 3 will be initiated in the future after the initial work on Part 1 and 2 has been completed) This part is intended to show fundamental aspects in the use of high performance liquid chromatography in combination with high resolution mass spectrometry and provides criteria for carrying out, validating and safeguarding non-target screening of small organic compounds in water by means of liquid chromatographic separation techniques followed by high resolution mass spectrometry. Aside from technical information pertaining to devices and potential contamination in sampling and measurements, this also includes data evaluation and quality assurance measures. The guideline is intended to assist the user in developing the method and interpreting the results.