Is Your Drinking Water Safe? If Not, Why Not?
The New York Times has run an extensive article about the nation's drinking water claiming that our public water is contaminated with thousands of chemicals, hundreds of which are "associated with a risk of cancer". It even has a link to the articles on which the claims are based. Unfortunately, or fortunately depending on your point of view, the evidence cited for the proposition that tap water is putting the citizenry at risk of cancer is pretty thin if that's all there is.
For example, under "Studies Regarding Illnesses and Drinking Water" (of which there are only eight) the only one to make a broad claim of tap water carcinogenesis is a 28 year old study titled "Cancer and Drinking Water in Louisiana: Colon and Rectum" which used the 1970 census to compare 692 rectal cancer deaths from 1969-1975 by where along the Mississippi River they and controls got their drinking water. The authors noted a small increase in risk as the source got closer to the Gulf of Mexico and suggested that the finding may have something to do with an increasing concentration of industries along the river as it approaches the Gulf. More importantly they wondered whether by-products of chlorination might have something to do with the finding.
The link suggests just four other papers that have cited the study and of those only two studied drinking water. Of the two, the first is a Canadian paper from 2000 (the first true Y2K victim I've ever run across - note: "Received 1999 Accepted 1900") which found no association with rectal cancer but a small one for colon cancer among males who drank "chlorinated surface water for 35-40 years".
Following the papers that cited the Canadian paper you quickly find another drinking water paper that finds a small protective effect for all leukemias combined, a large protective effect for chronic lymphocytic leukemia and a small but significant association with chronic myeloid leukemia.
The other papers are similarly all over the place and there appears to be no consensus that U.S. drinking water is a cause for concern about cancer from the perspective of chemical contaminants.
On the other hand, there's a growing body of literature associating drinking water contaminated by microorganisms with cancer. There's a new one discussing the waterborne transmission of helicobacter pylori to be published in next month's Journal of Water and Health and then there's this alarmingly titled paper in the same journal: "Free-living amoebae, Legionella and Mycobacterium in tap water supplied by a municipal drinking water utility in the USA"
It's unclear why the NYTimes focused on trace levels of chemicals as a cause for concern when there does appear to be something to be worried about when it comes to bugs in our water.
