The European water framework directive (WFD) states that measures should be taken to improve the quality of water bodies, to prevent further required extension of current (drinking) water treatment. Hence, for water managers it is of key importance to evaluate and report the quality of water and the level of purification treatment that is required. For this purpose a novel framework of indices is defined. The definition of the indices allows the inclusion of new, emerging substances. The indices can be calculated based on micropollutant characteristics alone and do not require any knowledge of specific purification treatment installations. Applying this framework of indices to water bodies provides an objective and reproducible manner to evaluate the required purification treatment level. The indices were calculated for water quality data for up to 600 micropollutants from five sampling locations along the river Rhine in the Netherlands. This revealed differences between the sampling sites (index values ranging from 145 to 273) and showed that for the river Rhine the required purification treatment level, as well as the underlying removal requirement and purification treatment effort, have not improved over the years, despite of the introduction of the WFD in 2000.


  • The Water Quality Index (WQI) can serve as water management tool for the European water framework directive.

  • It includes novel and upcoming micropollutants (MP).

  • It can be assessed integrally as well as separately on removal requirement and purification treatment effort of MP.

  • It is based exclusively on characteristics of MP.

  • The WQI indicates no improvement in water quality since 2000 in the river Rhine.

Graphical Abstract

Graphical Abstract
Graphical Abstract
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Supplementary data