This research is a study of Bangkok's sanitation system based on quantitative analysis of water and wastewater flow focusing on domestic sector. Nitrogen was quantified and assessed its distribution by Material Flow Analysis MFA. Field surveys and questionnaires for 300 households were conducted within three zones of Bangkok city inner city, urban fringe, and suburban. Nitrogen flow analysis revealed that the main pathways of nitrogen for greywater and blackwater were to sewerage system and onsite sanitation system OSS, respectively. With treatment facilities, wastewater from households was distributed into four facilities: OSS 44.51% N; decentralized wastewater treatment plants WWTPs 0.18% N; centralized WWTPs 4.80% N and septage treatment plants (STPs) 0.64% N. Simultaneously, nitrogen discharge to environment could reduce through OSS, decentralized WWTPs, centralized WWTPs and STPs from 26,011 to 4,540 ton N/year or at 82.55% reduction. In aspect of without treatment facilities, the remaining of wastewater was distributed to environment at 45.49% total wastewater from household. At the urban fringe zone, large wastewater flowed to environment without treatment 27.41% total wastewater from household. Meanwhile, septage was represented an important nutrient source. Non-treated septage distributed large amount of nitrogen 32.17% N with its small amount of flow into environment 1.92% total wastewater from household. Combinations of four treatment facilities including the OSS, decentralized WWTPs, centralized WWTPs and STPs were proposed as scenarios to reduce the existing discharge of 28,379.2 ton N/year to the environment. With the existing treatment facilities and practical scenario for each zone, nitrogen discharge could be reduce to 7,559.7 ton N/year 73.36% reduction with the strategies of centralized WWTPs for the inner city zone, the combination of decentralized and existing centralized WWTPs for the urban fringe zone, OSS for the suburban zone, and septage collection to STPs for all zones.