A method for the continuous meausrement of radon in water, which uses a ionisation chamber, is described. The ionisation current (in the range of 10-11 A) is strictly proportional to the radon content in the water. It is supposed that there is a connection between the radon concentration in groundwater and springs and earthquakes. We therefore think that this connection might be used for earthquake prediction. A research project for that purpose had been started in Austria.