The overall goal of this research is to develop water quality monitoring systems, an intelligent sensor network that combines ontology, the agent system, and the SWE technology, provide realistic dynamic information. The system is designed to simulate the water quality monitoring system at the Long De Industrial Park in Yilan County. The focus of this paper is the design and implementation of the ontology. We use Protege as the editing software to describe and present the concepts and attributes in the domain knowledge as well as the relations between them in order to support automatic interpretation and action by the agent system. In this paper we first probe Water Quality Sensor to describe the meaning of ontology and explore methods for building the ontology. Finally, we provide the implementation of the ontology and our conclusions for fellow researchers in this subject.