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WaterAid in Pakistan just completed first year of a R&D project in collaboration with National University of Science and Technology. The goal is to improve and upgrade current WASH systems and develop new techniques and prototypes for water and sanitation in rural and peri-urban areas of Pakistan. These solutions are expected more sustainable, low cost and viable in addressing WASH issues faced in developing world. Under this partnership, one of the research carried out was to develop low cost on-site wastewater treatment system for rural areas of Pakistan. In this study, a modified septic tank with filter, termed as the anaerobic baffled reactor (ABR) coupled with anaerobic peat filter (APF) was developed. The study aimed at providing an onsite domestic wastewater treatment that was able to produce an effluent quality meeting the national environmental quality standards (NEQS) (Pak-EPA). The system was operated at HRTs of 48, 36 and 24 hours where optimum HRT was found to be 25 hours based on the treatment performance indicators. The ABR and ABR-APF was able to produce an average removal of 80, 76, 80, 92% and 89, 88, 90, 99% in terms of COD, BOD5, TSS and faecal-coliforms, respectively. The average removal percentage for nutrients (nitrite, nitrate, and phosphate) was found to be varying between 30-70%. The system requires no energy and works under the natural gravity hence it is suitable for countries like Pakistan suffering from energy crises.