A point-of-use waterborne radon-222 (222Rn) survey of a small Iowa town was performed to determine the cause of unnaturally high waterborne 222Rn concentrations in the municipality. The source of the elevated 222Rn concentrations was a newly discovered reservoir of waterborne 222Rn originating from distribution-system radium-226 (226Ra) adsorbed internal pipe scale deposits. Because the proposed national drinking water regulations for 222Rn require sampling at the origin of the distribution system rather than at the point of use, the proposed scheme for collection of water samples may not represent actual consumer waterborne 222Rn exposure in all cases.