When it comes to carcinogens that industrial plants dump into the water, the government generally takes a hard line on levels of public exposure.
But public health officials accept far greater risk with the naturally occurring radioactive substance radon, which enters homes from the ground and underground aquifers through basements and water pipes.
The radioactive gas, the dangers of which have been known for decades, is so prevalent in nature that getting to the standard risk level would be nearly impossible.
New Jersey and Pennsylvania are among a number of states plentiful in radon. For more than a decade, state and federal governments have held off in regulating how much of the gas should be allowed in drinking water. The New Jersey Department of Environmental Protection is analyzing data as it considers its next step.