When mapping out strategies for an integrated water resource management in urban areas the precipitation-conditioned influences on the quality of waters available as resource are considered in an increasing manner. Amongst water discharges from urban areas, combined sewer overflows (CSO) represent a particular impact on waters due to their dynamic character. To assess CSO impacts, especially for an integrated modelling of sewer system and surface waters, quantity and quality data from the interface combined sewer overflow is needed. A monitoring concept for CSOs in Berlin was developed in the context of the project Monitor-1 by the KompetenzZentrum Wasser Berlin. In 2009, this concept will be realised in cooperation with the Berlin water authority and the utility Berliner Wasserbetriebe. When planning and preparing a monitoring an important aspect is, adjacent from the evaluation of possible locations, the selection of suitable measuring techniques. For this, extensive tests of different online measurement techniques from reputed manufacturers were accomplished at a test facility at the TU Berlin. Apart from questions such as accuracy, response behaviour at suddenly arising load peaks or dilutions and available measuring intervals, particularly aspects of calibration, cleaning and management of the sensors were evaluated. The influence of the calibration was especially examined with the ion-selective sensors (ISE). The question was pursued, how the sensors must be calibrated to offer the greatest possible accuracy for the generally very low concentrations in surface waters and the occurrence of a sudden and precipitous rise of concentration in the case of the start of the CSO. Ammonium and nitrate were also supplemented with chemicals besides the stockpiling with waste water. An important finding was that generally all sensors are applicable for the measurement task.