Even ‘Safe’ Tap Water Can Have Cancer-Causing Contamination

When you turn on your tap, you trust that the water that comes out is safe to drink. But it’s not just community water systems with high levels of contaminants that put people’s health at risk, suggests a new study. Even community water systems that meet national drinking water standards can carry health risks, especially when you add up the health effects of the individual contaminants in the water. Researchers show evidence that chemicals in US drinking water may be responsible for over 10,000 cancer cases over an 8-year period. “Risk assessments have been typically conducted for individual drinking water contaminants such as arsenic or nitrate, or for small groups of related chemicals such as disinfection byproducts or metals,” they write.

Even ‘Safe’ Tap Water Can Have Cancer-Causing Contamination

“Here, we present the first application of the cumulative cancer risk framework to a drinking water dataset for the entire United States.”Evans’ team shows evidence that the cumulative cancer risk associated with contaminants in drinking water in the US is between 1-in-1,000 and 1-in-10,000, meaning that out of either 1,000 or 10,000 people, there would be one case of cancer. According to the team’s research, this level of risk varies depending on where you live in the US — hence the range.

Regulation needs to keep up with the science

Evans says their analysis can inform how the government regulates water contaminants in drinking water. But it can also help educate people about their exposure risks. “This research is not just for regulators and policymakers,” Evans said. “We want individuals to know that the legal [contaminant] levels aren’t necessarily safe.”He also thinks even more needs to be done to protect our drinking water, especially since the EPA has water contaminant regulations for only a small percentage of the tens of thousands of chemicals in society.

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“When in doubt [about the health risks], if there is a substance that’s in our drinking water supply, it ought to be monitored for,” said Kauffman, who wasn’t involved in the study. “And if the science is there, there should be an MCL established for it.”The EPA issued a heailt advisory earlier this year that set a lifetime exposure limit for these chemicals. But the agency hasn’t yet passed an enforceable drinking water standard that covers them.

Notably, as the maps below show, they identified that municipal water drawn from the ground generally carried a lower risk than water from surface sources like reservoirs.

These maps show the cumulative cancer risk for municipal water drawn from the ground (top) versus water from surface sources (bottom).
These maps show the cumulative cancer risk for municipal water drawn from the ground (top) versus water from surface sources (bottom).

The word ‘cumulative’ comes into play when looking at a whole lifetime of exposure. So these numbers aren’t for a day or a week of drinking contaminated water, but a whole lifetime. Thus, improving water quality at the tap and investing in measures for source water protections represent opportunities for protecting public health and decreasing potential disease incidence due to environmental pollution.

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