The Nakdong River being used as drinking water sources for the Busan metropolitan city has the vulnerability of water management due to the fact that industrial areas are located in the upper Nakdong River. This study used emergy analysis method to evaluate ecological-economics of water treatment systems of D water treatment plant (WTP) where located in the downstream of the Nakdong River. The emergy methodology is a system evaluation tool that uses energy as the common currency to compare different resources on a common basis. Emergy yield ratio (EYR) and emergy sustainability index (EmSI) of D WTP were 1.16 and 0.18, respectively. It means not resources and sustainable system but consumer goods and not sustainable system. Ratio of emergy benefit to the purchaser (EBP) shows 2.7 times higher than economic costs. To change the weak water source and situations we need to diversity water intake.