The radon-222 content of water especially is of interest considering aspects of radiation protection or techniques to investigate hydrologie characteristics of aquifers using radon-222 as a natural tracer. Sampling and measurement of radon in groundwater are complicated by the high volatility of the gas. A method including sampling techniques (pumping, flushing time, filling arrangement and sample transportation) and rapid analysis of radon with high reproducibility was investigated and tested. The measurement is based on extraction concentration of radon-222 and liquid scintillation spectrometry. The detection limit of this method is about 0.05 Bql⁻¹. By means of α/β discrimination it can be confirmed that radon-222 is the origin of the measured radioactivity.