The water system provides many services to society; industries, municipalities and agriculture all withdraw, use and return water and demand a water quality fit for the intended purposes. Both global production of chemicals and global water withdrawal grow faster than human population. This implies increased chemical threats to water, and creates a strong driver for mitigation to protect human health, ecosystem integrity and ecosystem services. Here we connect the perspectives of the water cycle and the chemical life cycle and review possible mitigation options. We categorize mitigation options in various stages of the chemicals' life cycle, taking various sectors and environmental pathways into account. More technologically oriented versus other types of mitigation options are discerned, and their relevance on spatial and temporal scale is discussed. We review various water treatment techniques in relation to physical–chemical properties of chemicals. Finally we discuss how a mitigation database can be used to assess the effectiveness of interventions, by coupling them to regional or global hydrological models. A solution-focused and systems-oriented perspective combined with a mitigation database offers a common perspective amongst actors on the effects for water quality of possible mitigation options throughout the chemical's life cycle, in various sectors and at various places in the water system. This can stimulate coherent implementation of effective mitigation options, cross-sectoral learning and further innovations to improve water quality.@en

Water authorities and drinking water companies are challenged with the question if, where and how to abate contaminants of emerging concern in the urban water cycle. The most effective strategy under given conditions is often unclear to these stakeholders as it requires insight into several aspects of the contaminants such as sources, properties, and mitigation options. Furthermore the various parties in the urban water cycle are not always aware of each other's requirements and priorities. Processes to set priorities and come to agreements are lacking, hampering the articulation and implementation of possible solutions. To support decision makers with this task, a decision support systemwas developed to serve as a point of departure for getting the relevant stakeholders together and finding common ground. The decision support system was iteratively developed in stages. Stakeholders were interviewed and a decision support system prototype developed. Subsequently, this prototype was evaluated by the stakeholders and adjusted accordingly. The iterative process lead to a final system focused on the management of contaminants of emerging concern within the urban water cycle, from wastewater, surface water and groundwater to drinking water, that suggests mitigation methods beyond technical solutions. Possible wastewater and drinking water treatment techniques in combination with decentralised and nontechnical methods were taken into account in an integrated way. The system contains background information on contaminants of emerging concern such as physical/chemical characteristics, toxicity and legislative frameworks, water cycle entrance pathways and a database with associated possible mitigation methods. Monitoring data can be uploaded to assess environmental and human health risks in a specific water system. The developed system was received with great interest by potential users, and implemented in an international water cycle network. © @en