Water Absorbent Mat and Filtration System (WAMFS): A Low-Cost Greywater Recycling Technology for Urban Water Scarcity and Climate Resilience in Karachi, Pakistan

Water scarcity and greywater pollution are growing challenges in urban areas of Karachi, Pakistan, where household wastewater is often discharged untreated into drainage systems. This preprint presents the Water Absorbent Mat and Filtration System (WAMFS), a low-cost greywater management concept designed to improve water capture, reduce wastage, and enable reuse for non-potable applications. The proposed system consists of a multi-layer water-absorbent mat placed over existing bathroom floor drains and a connected filtration unit. The mat includes a stainless steel grid for debris interception, a coconut coir absorbent layer, hemp-based wicking channels for water transport, and a perforated recycled rubber base for structural support and controlled drainage. This configuration enables greywater to be intercepted at the drain level and directed into existing household drainage systems without requiring major structural modifications. Collected greywater is treated through a filtration process involving gravel, sand, activated charcoal, and a final disinfection stage using chlorine or ultraviolet (UV) treatment. The treated water is intended for reuse in non-potable applications such as cleaning and irrigation, reducing dependence on freshwater sources. A key feature of the system is its retrofit compatibility, allowing installation in already developed residential buildings. The design also supports potential integration with community-level greywater management systems in water-stressed areas. Unlike conventional greywater systems, WAMFS integrates passive drain-level interception with modular filtration, enabling decentralized retrofit deployment in existing households. Overall, WAMFS presents a modular and scalable approach to decentralized greywater interception and treatment, supporting sustainable urban water management and aligning with Sustainable Development Goal 6 (Clean Water and Sanitation). Preliminary estimates suggest that if implemented at household scale, the system could conserve up to 30 liters of water per household per day, amounting to over 10,000 liters per household annually. Further experimental validation is recommended to assess system performance under real-world conditions.