In this paper, we introduce various attempts to transmit sensor data efficiently for design of a water quality monitoring system under the USN environment. The representative methods are the sensor management on a sensor node and the clustering on a sink node. The sensor management includes controls of sensing intervals, data accumulations, and data transmissions. And the clustering is one of efficient data compression methods using data mining technology. From the experimental results we confirmed that the proposed transmission method using the sensor management and the clustering outperformed common transmission method.