The fountain pipe is a metal cylinder open at the bottom with a small whistle hole in the otherwise closed top. The outside of the cylinder is divided by circumferential notches at a distance of 1 cm. The graduation begins below the cylinder's whistle hole. The fountain pipe is hung down on the surface of the water on a measuring cord or tape measure. When immersed in the water, water penetrates the cylinder from below. This displaces the air through the whistle hole, creating a sound like a labial whistle . Once the sound is heard, the pipe must not be submerged any further. The depth from a measuring point, for example the surface of the terrain, to the water level results from the sum of the length of the measuring cord or the measuring tape and the number of not water-wetted notches in the well pipe. The procedure is suitable for depths of up to 30 m; at greater depths, the whistling tone is increasingly difficult to hear. The measurement accuracy is 1 cm, which corresponds to the distance between the outer rings. The fountain whistle has almost completely disappeared from professional use with the introduction of the cable light plumb bob .
Another application is the measurement of oil layers on water layers in the ground. In the event of accidents or tank leaks, oil can reach the groundwater body and then float on the groundwater. In this case, the oil level is measured in a test borehole with a well pipe and the water level is measured with a light soldering cable (which measures according to the conductivity principle). The difference is the thickness of the oil layer.