This document delves into wastewater challenges and opportunities. A prime example for innovative and sustainable solutions of man-made problems are so-called green filters, which GNF has planned and built together with various engaged project partners in Latin America. These filters offer cost-effective solutions for wastewater treatment and thus not only benefit the population, but also protect sensitive lakes and their flora and fauna, from the Caribbean to the Andes highlands. Here, you will find several examples of projects concentrated on green filters. It highlights innovative strategies, case studies, and actionable steps to address pressing environmental and sustainability issues. This document is a valuable resource for stakeholders seeking to understand and implement solutions in wastewater contexts.