Inhalation of escaping radon from groundwater comprises the largest part of radiological hazard from groundwater radionuclides in the uranium and thorium series. Groundwater containing 1.5 mg dm uranium and 3 kBq dm radon activity concentration supplied an ordinary bathroom of 15 m in a home. Using the showerhead, atmospheric levels of radon activity in the bathroom exceeded 100 kBq m within a period of about 1 h.