Recently, we must make public enterprises cost effective and environmental friendly. Methods of environmental conservation for water pollution are not exception. We examined environmental quality of a small river which was improved by the methods of environmental conservation. The conservation methods are sewer construction, the spread of private sewerage treatment tank for household wastewater, stream purification system in the flood plain and flow back system of advanced treated water for upstream of the river in a sub-urban area. And we estimated the costs and environmental loads of the environmental conservation for entire their life cycle. Moreover, we investigated the relation between environmental quality and cost or environmental loads. Therefore, we presented more cost effective and more environmental conscious methods of environmental conservation.