Really hot water.

Sometimes, water heaters do more than the obvious. While they heat water, they also collect a little uranium, creating deposits of radioactive scale inside their tanks. That's what South Carolina researchers have discovered in a community with the dubious distinction of having water that's naturally laced with among the highest concentrations of uranium ever reported in groundwater: 10,000 micrograms per liter.

Uranium concentrations in 50 residential wells near Simpsonville exceed federal drinking water standards by a factor of 300, Van Price of the University of South Carolina in Columbia and his colleagues reported in Denver at a meeting of the Geological Society of America last November.

In homes receiving some of the most contaminated water, uranium concentrations fell by about 23 percent as water passed through heaters, Timothy A. DeVol and Richard L. Woodruff Jr. of Clemson University now find.

Their calculations, presented in the December 2004 Health Physics, indicate that residues from the water left each heating tank with up to 69 grams of uranium, depending on the tank's age and the household's water use.

Although the radioactive tank deposits pose little or no risk to homeowners, DeVol says, they do justify classifying the water heaters as naturally occurring radioactive waste (SN: 10/26/91, p. 264). Such materials can pose hazards if the tank's metal is later scrapped and recycled. For now, they're not subject to regulation by the federal government or most states. --J.R.