Perchlorate was found in the water supply of three Iowa towns Investigators were trying to determine why the toxic chemical was in the water in Hills, Napier and Ewart.
Families in the Hills area were offered bottled water because there were high concentrations of the contamination.
Investigators say they have no idea where the perchlorate came from.
Perchlorate is both a naturally occurring and man-made chemical. Most of the perchlorate manufactured in the United States is used as the primary ingredient of solid rocket propellant. Wastes from the manufacture and improper disposal of perchlorate-containing chemicals are increasingly being discovered in soil and water.
Several types of treatment systems designed to reduce perchlorate concentrations are operating around the United States, reducing perchlorate to below the 4 ppb quantitation level. Biological treatment and ion (anion) exchange systems are among the technologies that are being used, with additional treatment technologies under development.