Today, demands on water quality are diverse and strongly differ by water use related criteria. Additionally, the complex topic of water quality is of increasing importance for citizens and is therefore often emotionally loaded by media. Surface waters are important ecosystems for biota. Additionally, they can serve as drinking water resources and have become increasingly important for recreational activities and tourism. Ground and surface waters hence deserve protection, which creates a need

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... r reliable water quality monitoring that produces high resolution and information-rich water quality data. Currently, European water quality is assessed under the water framework directive (WFD), which has shown that water quality needs to be improved in many catchments. Nowadays, water quality data are based on fixed stations with monitoring conducted on predetermined dates and focusing on a more historically relevant list of classic water quality indicators. This often generates a biased and insufficient picture of the water quality. Understanding system dynamics to meet the needs of divers demands on water quality between catchments and water bodies requires a more flexible approach, while producing more meaningful data. Classic water quality indicators, such as inorganic ions, are often not source specific and too general as they have myriad different anthropogenic and natural origins. They are only to a minor extent suitable for reliable source apportionment, to understand system dynamics and risk assessment. In contrast, sources of micropollutants such as pharmaceuticals, lifestyle and personal care products, pesticides, household chemicals etc., are strongly related to anthropogenic activities. These in turn are very source specific, bear neglectable natural background concentrations, and hence can act as powerful, reliable and unbiased indicators. This thesis gives a comprehensive and systematic overview of (micro)pollutants used as indicators in the aquatic environment over the last decades. Successfully exploiting micropollutants as indictors starts with appropriate sampling procedures, sample storage and analysis. These are essential steps in providing reliable data. This review is structured into the qualitative, semi-quantitative and quantitative use of indicators and presents a guide on how to decide for a suitable set of indicators. Besides suitable sets of indicators, a water quality monitoring strategy, adjusted to the catchment needs and producing reliable and information-rich data, is im-