Tap Water Contains Carcinogens, but Don’t Worry Too Much

A new study found that tap water pollutants can cause 100,000 cases of cancer in the United States each year . While the numbers may be correct (it’s hard to say for sure), that doesn’t mean you should worry too much about tap water.

These results are “in the same range of cumulative cancer risk as air pollution … but that doesn’t mean you shouldn’t go outside or stop breathing air,” said Daniel McCurry, an environmental engineering researcher who studies drinking water. systems that did not take part in the study.

Researchers working with the Environment Working Group (which I personally have always been very suspicious of ) published a report that summarized the potential cancer cases caused by various pollutants found in tap water. For example, 0.004 micrograms of arsenic per liter of water is estimated to provide one in a million cancer risk. (These numbers are mostly based on animal studies; it’s impossible to know exactly how many real-life cancers in humans might be associated with tap water.)

Based on the US population, the authors estimate that this is 45,000 cancers per year. Other pollutants, including by-products of chemicals added to disinfect water, pose lower risks, with a total of about 100,000 cancers in a lifetime, potentially associated with tap water.

What to do if tap water bothers you

Unfortunately, there are not many alternatives. Tap water is cheap and safe. People who design and study water systems (McCurry, for example) can use results like this study to understand population- level risks, but this does not provide practical advice for you and me.

First, the main carcinogen in the study is arsenic, which is not produced during water treatment. It is naturally present in water, depending on the geology of the area where the water was collected. If you’ve switched to well water or bottled spring water, you don’t have to avoid it.

Then, if you do use bottled water, you also have to worry about microplastics and chemicals from plastic bottles getting into your water. Plus, most of the bottled water is just tap water anyway.

One possible solution is to filter your tap water. Not all filters remove all contaminants, but a 2017 study found the ZeroWater Pitcher did better at removing arsenic than other filter pitchers. Most filters use activated carbon and can remove disinfection byproducts, which were also named in the study.

But with or without a filter, we are looking at very little risk: one in 10,000 if the numbers are correct (and there is a lot of uncertainty in those numbers). McCurry says he personally drinks unfiltered tap water, but he has colleagues who filter theirs. So filter if you like, but don’t worry anyway.


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