Radon water to air transfer measured in a bathroom in an energy-efficient home with a private well

Monthly measurements of radon in kitchen and bath tap water along with indoor air concentrations were made from 1994 to 1996 in an energy-efficient home with a private well. The well supplies all water to the home. The radon in cold and hot kitchen water averaged 69±2 and 52±2 Bq l(-1), respectively. Radon in cold and hot water from the bath/shower room shower head averaged 60±1 and 38±2 Bq l(-1), respectively, whereas hot water collected in the shower at the tub base averaged 5±1 Bq l(-1) or a 92% radon loss to air. While the calculated transfer factor of 1/10,000, i.e. radon concentration in air to radon in water, conventionally applies to the whole house, measurements for the specific water release during showering in a bathroom exhibit a larger transfer factor of 1/2300, due to smaller room volume.