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.
In a report last year, the scientific body charged with this task, the New Jersey Drinking Water Quality Institute, recommended that homes and schools have mandatory air tests - nearly all radon-related deaths come from lung cancer - and a maximum level for drinking water set at a point where an additional 1 in 2,000 people would develop cancer over a lifetime of exposure.
That's 500 times the accepted risk for the standard industrial pollutant.
The DEP is reviewing the institute's report and will conduct its own inquiry, said John Plonski, assistant commissioner for water resources. "We are taking this very seriously," he said.
There is no time frame for when possible radon regulations would be in place, Plonski said.
Scientists estimate that more than 200,000 New Jerseyans - primarily in the northwest, but also in parts of Gloucester County - are exposed to radon levels at or greater than the prescribed level.
Over the last two decades, public water systems have at times reached levels more than 25 times the allowable radon exposure recommended to DEP, according to the institute's data.
That's because excess radon is found in underground aquifers, not in water drawn from rivers, where the gas escapes.
In areas where radon is known to be prevalent, some residents intentionally stand back when they turn on the faucet or shower, which sends the radioactive gas in the water into the air. But many never think about it until they're selling their home and are requested by the buyer or mortgage company to have a radon air test performed. The tests are not required in Pennsylvania or New Jersey, according to state environmental officials.
"Most people don't realize because it's odorless and colorless," said Ed Knorr, a self-employed home contamination inspector and environmental activist in Gloucester County.
"When I tell them they have a radon problem, some will turn around and look at it as being a serious concern. Others will say, 'Oh, well, it hasn't killed me yet.' Until there's a real good program put out there, most people are never going to know."
To install filtration systems and bring New Jersey's water-distribution systems in line will cost about $79 million over 20 years, according to the institute's report. That doesn't include private wells, upon which about 40 percent of the state relies.
In the macabre math of public health, that works out to $400,000 for each person whose death from breathing and drinking radon would be prevented over 70 years, according to an institute analysis.
The cost of bringing down radon in homes with private wells is likely to be high as well, with home filtration systems running between $3,000 and $5,000, Knorr said.
With New Jersey's economy in peril, environmentalists are skeptical that Gov. Christie will move forward on radon regulation.
Since taking office in January, Christie's administration has delayed a number of proposed environmental regulations, including a decision on perchlorate, a chemical found in fertilizer and rocket fuel that has been found in drinking water in North Jersey.
The U.S. Environmental Protection Agency first proposed regulating radon levels in groundwater in 1999. The outcry was intense, with water officials across the country portending massive rate increases. A decade later, the agency's proposed rule still is not finalized, an EPA representative said.
Pennsylvania, which has elevated radon levels across most of the eastern half of the state, does not regulate radon and also is awaiting a decision by the EPA, said a representative for the Pennsylvania Department of Environmental Protection.
The fact is, radon is everywhere - in the air, the water and in the ground. In many areas, just breathing will increase the cancer risk in more than one in a million people, said Judith Klotz, a public health professor at Drexel University who helped write the institute's report.
So the question becomes: What level is acceptable at what cost?
"There is a background risk of developing lung cancer from just living on this planet," Klotz said. "We looked at distribution of radon in the groundwater, the cost of treatment, the risks at various levels."
A limit of one additional cancer death per 2,000 people "seemed a reasonable recommendation," she said.
Bill Wolfe, the New Jersey director of Public Employees for Environmental Responsibility, has been a frequent critic of the DEP since he left the agency a few years ago.
The process of weighing expense against human life is a job for the Legislature, not one the state's scientists should undertake, Wolfe says.
"DEP is supposed to base its decision on science. If they propose a law that is to bankrupt the state, it's not their job to decide whether that's right or not," he said. "If it's going to be $12 more a month on the water bill, then let's have the debate."
It's difficult to gauge how the public would react in choosing between high levels of radon in groundwater and increased water bills, said Edward Christman, an environmental health professor at Columbia University.
He has worked on groundwater issues for decades and believes public reaction to potential loss of life has less to do with quantifiable risk than the form death might take.
"The public perception of this risk is small because [radon] doesn't smell, it doesn't kill you right away," he said. "Driving a car is a higher risk, for instance. But it's a risk the general public is willing to accept without too much worry."