In Hungary there are borehole tiltmeters used for monitoring tectonic movements and landslides. These investigations need long time continuous measurements. The Model 722A tiltmeters of Applied Geomechanics Inc. are fastened to the ground by tamped sand in the borehole. In some cases the boreholes become untight and it was thought that in this case the ground water seeping into the borehole could loosen the tamped sand causing a bad coupling between the tiltmeter and the ground. It was proved by laboratory test that the ground water and the variation of its level does not change the coupling of the instrument to the ground. In this paper the description of the test made at the Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences and the results of the measurements are given.