Urban Cascade

By 2040, 33 countries will face extreme water stress, impacting food production and water supply for growing populations. Currently, 70% of water use is for irrigation. Meanwhile, the average person generates 200L of greywater daily - coming from sinks, showers and washing machines - a water source rich in nitrates and phosphates, ideal for agriculture, but often wasted. How can we repurpose household greywater for irrigation while improving the built environment through nature-inspired designs, innovative solutions, upcycled bio-based materials, and computational design optimization?

Through material research, we found chitosan - a biopolymer extracted from mollusks and crustaceans' shells - as a sustainable way to remove toxins in greywater. We upcycled mussel shells - a local abundant waste in Spain - into a bio-based material with chitosan. After many experiments, the material’s functionality was understood, and computational design and optimization were used to create tiles from it. These tiles are designed to cascade water across their surfaces, removing heavy metals and suspended solids. To make water suitable for irrigation, we integrated constructed wetlands, which can eliminate remaining contaminants through the plants. The project expands to a landscape intervention in Vigo in Galicia, Spain - one of the world’s largest mussel producers and a region facing seasonal water stress-. Within Vigo, Navia Park was chosen due to its central role, lack of vegetation, and polluted water feature, making it an ideal site for transformation. The design turns Navia Park into a water treatment facility and a food production center. Greywater from surrounding buildings flows into the park, cascading through the walls and filtering tiles, before reaching constructed wetlands placed in previously arid areas. The treated water is then used for irrigation. To power the system and enhance food production, solar canopies are installed across the site, while elevated decks connect the fields, offering recreational spaces and ensuring the system’s efficiency. The final design ensures sufficient water for irrigation while also returning treated water to the context. Urban Cascade fosters water and food security, strengthens community engagement, promotes biodiversity, and mitigates the urban heat island effect through the integration of nature-inspired solutions.