The water level is a significant data for hydrology analysis. Nowadays, the ultrasonic gauge and radar gauge has been adopted to replace float gauge and pressure gauge, the previous equipment. Compared with bubble gauge, the after-mentioned equipments are inferior due to the sundry limitations, such as site condition, economic condition and environment condition. Bubble gauge is much higher convenience than others, to insert the measuring tube into underwater along pier or wall is the only preparation, the installation is much simpler; furthermore, to exchange abolished measuring tube is feasible, maintenance fee and sampling location is no longer to be consideration. For The experiment precision, PVC pipe was adopted to measure the water level of Taiwan rivers and dams, and the water density was adjusted to enhance higher accuracy. Bao-er dam and Beishi River is the major subject of extralaboratory testing, for long time observation, drops were occurred in measuring tube and resulted to unstable data; however, this phenomenon occurred in Bao-er dam experiment only.