To accelerate the transition to a circular economy, the European Commission (EC) promoted alternative water resources in the Horizon 2020 Framework. To increase water use efficiency and reuse, the call CE-SC5-04-2019 funded five different projects (B-WaterSmart, WIDER UPTAKE, REWAISE, ULTIMATE and WATER-MINING). These five projects run from 2020 to 2025, with a total budget of 84 M€, and EU contribution of 71.5 M€, and share the objectives of identifying alternative water sources, reducing water consumption, increasing use efficiency, recovering valuable materials from water, producing carbon-free water cycles, and increase resilience to climate change. To leverage the resources from EC wisely, the five coordinators decided to share common knowledge, promoting synergies and avoiding reinventing the wheel. This resulted in the creation of a cluster called CIRSEAU, to connect 143 partners in more than 20 countries, reaching almost all members stated of the European Union (EU), in addition to countries like India or Ghana outside the EU. Building on the alliance formed to foster cross-promotion, communication alignment, and impactful outreach for the five projects funded under the EU research call on building a water-smart economy and society (CE-SC5-04-2019). To reach the outcomes of this CSA, additional experts and partners have been asked to complement experience and competence of CIRSEAU. This consortium brings together 10 partners from 6 countries (BE, DE, ES, GR, NL and NO) to provide multidisciplinary expertise and trans-nationality required to foster cross-promotion, communication alignment, and allow impactful outreach to public authorities, policy makers, and standardization bodies. The main objective of the CSA is to build a collaborative ecosystem that generates strong synergies among the Circular Water Economy Community formed across EU projects, and to expand the CIRSEAU cluster to enhance market uptake, collaboration and knowledge sharing.