The major objective of the survey was to describe the distribution of waterborne 222Rn concentrations in Iowa's private well-water supplies. Well-water samples were obtained and analyzed for 222Rn from a random sample of 352 Iowa wells. The well-water 222Rn concentrations for the well sites were log normally distributed and ranged from background concentrations to 87 Bq L−1 with a median value of 12 Bq L−1. The arithmetic mean 222Rn concentration for the sites was 16 Bq L−1+ −13 Bq L−1 The geometric mean 222Rn concentration was 12 Bq L−1 with a geometric standard deviation of 2.2. Over half of the samples (52%) exceeded 11 Bq L−1. Both well depth and indoor air 222Rn screening levels correlated with waterborne 222Rn concentrations; however, these correlations had very little predictive value. Glacial drift aquifers tended to have the highest 222Rn concentrations, although there was significant variance of 222Rn concentrations within all the aquifer classifications. In light of the estimate that 370 Bq L−1 of 222Rn in water may lead to 37 mBq L−1 in indoor air, the contribution of wellwater derived indoor air 222Rn is minimal compared to ground sources in Iowa.