Investigating wastewater management matters: in many OECD countries, the conventional centralized system is reaching its limits. Alternative decentralized options exist. Some directly affect citizens with in-house wastewater treatment. Involving citizens in decision processes would legitimate the outcome and facilitate implementation. However, citizen participation is challenging because they are numerous, and need to learn about the topic and construct their opinion. To include citizens, we propose an innovative online survey based on Multi-Attribute Value Theory (MAVT). Citizens receive value-focused information, and can communicate their preferences, captured as weights assigned to objectives. We collected quantitative and qualitative data, and elicited preferences from 184 young Swiss citizens, who will have to live with the decision outcome. In addition to reporting on insights for wastewater management, we assessed our survey, i.e. whether respondents learnt about the topic, constructed preferences, and understood the requirement to think in terms of objectives. Water quality and health protection mattered the most. The objectives directly concerning the respondents (time demand, attractiveness) were the least important. The best-ranked option in the subsequent Multi-Criteria Decision Analysis was a decentralized source separating system with dry toilets. Respondents were unaware that such decentralized options exist, indicating that learning about the topic occurred. Preferences were mostly newly constructed from no opinion, or pre-existing ones were reinforced. Our value-focused online survey helped citizens to understand the complex decision and construct their preferences. Swiss decision-makers, and beyond, should not be scared of a paradigm shift in wastewater management: the young generation seems ready to decentralize.