Radon gas with chemical symbol Rn222 is the heaviest element radioactivity, colorless, odorless, tasteless, heavy and noble. Radon naturally in rocks and soils and waters is available and because there is no affinity to plead easily by soil and water molecules into the air and is moving. Radon enters the body with breathing, eating and drinking.Alpha, which is emitted from radon and other nuclear radiations, sent by its daughters nucleus, serious damage to human respiratory and gastrointestinal system brings, so after smoking, the second risk factor in lung cancer is radon radiation. Radon gas density varies due to factors such as temperature, air pressure, humidity and changes in ground layers. As a result, radon gas densities in the seasons are different. In this research, water radon concentration of 10 point Shandiz area in different seasons of the year with the help PRASSI system is measured. Fortunately, the results show that only two samples of drinking water are higher than normal density Bq / l 11.1 in the fall.